Add support for the doublestroke package

This commit adds the mathed command \mathds that selects a
font more appropriate than \mathbb for typesetting the
mathematical symbols for the natural (N), whole numbers (Z),
rational numbers (Q), real numbers (R), complex numbers (C),
and some others.

As in the \mathbb case, only capital letters are supported,
but in addition one can also typeset a symbol often used for
representing the indicator function (\mathds{1}) and the
letters a, h, k.

Fixes bug #11887.

lib/symbols

@@ -118,6 +118,7 @@ Bigggr            big         none        hiddensymbol
 mathnormal        font        mathmode  inherit  medium   up  math
 frak              font        mathmode
 mathbb            font        mathmode
+mathds            font        mathmode
 mathbf            font        mathmode
 mathcal           font        mathmode
 mathfrak          font        mathmode

lib/ui/stdtoolbars.inc

@@ -423,6 +423,7 @@ ToolbarSet
 		Item "Italic	\\mathit" "math-insert \mathit"
 		Item "Typewriter	\\mathtt" "math-insert \mathtt"
 		Item "Blackboard	\\mathbb" "math-insert \mathbb"
+		Item "Double stroke	\\mathds" "math-insert \mathds"
 		Item "Fraktur	\\mathfrak" "math-insert \mathfrak"
 		Item "Calligraphic	\\mathcal" "math-insert \mathcal"
 		Item "Formal Script	\\mathscr" "math-insert \mathscr"

src/FontEnums.h

@@ -45,6 +45,8 @@ enum FontFamily {
 	///
 	MSB_FAMILY,
 	///
+	DS_FAMILY,
+	///
 	EUFRAK_FAMILY,
 	///
 	RSFS_FAMILY,

src/FontInfo.cpp

@@ -493,6 +493,7 @@ string getFamilyCSS(FontFamily const & f)
 	case CMEX_FAMILY:
 	case MSA_FAMILY:
 	case MSB_FAMILY:
+	case DS_FAMILY:
 	case EUFRAK_FAMILY:
 	case RSFS_FAMILY:
 	case STMARY_FAMILY:

src/LaTeXFeatures.cpp

@@ -1158,7 +1158,8 @@ char const * simplefeatures[] = {
 	"xskak",
 	"pict2e",
 	"drs",
-	"environ"
+	"environ",
+	"dsfont"
 };
 
 char const * bibliofeatures[] = {

src/frontends/qt/GuiFontLoader.cpp

@@ -36,8 +36,8 @@ using namespace std;
 using namespace lyx::support;
 
 QString const math_fonts[] = {"cmex10", "cmmi10", "cmr10", "cmsy10",
-	"esint10", "eufm10", "msam10", "msbm10", "rsfs10", "stmary10",
+	"dsrom10", "esint10", "eufm10", "msam10", "msbm10", "rsfs10",
-	"wasy10"};
+	"stmary10", "wasy10"};
 int const num_math_fonts = sizeof(math_fonts) / sizeof(*math_fonts);
 
 namespace lyx {
@@ -78,6 +78,7 @@ SymbolFont symbol_fonts[] = {
 	{ CMEX_FAMILY,  "cmex10", "-*-cmex10-*-*-*-*-*-*-*-*-*-*-*-*" },
 	{ MSA_FAMILY,   "msam10", "-*-msam10-*-*-*-*-*-*-*-*-*-*-*-*" },
 	{ MSB_FAMILY,   "msbm10", "-*-msbm10-*-*-*-*-*-*-*-*-*-*-*-*" },
+	{ DS_FAMILY,    "dsrom10", "-*-dsrom10-*-*-*-*-*-*-*-*-*-*-*-*" },
 	{ EUFRAK_FAMILY,"eufm10", "-*-eufm10-medium-*-*-*-*-*-*-*-*-*-*-*" },
 	{ RSFS_FAMILY,  "rsfs10", "-*-rsfs10-medium-*-*-*-*-*-*-*-*-*-*-*" },
 	{ STMARY_FAMILY,"stmary10","-*-stmary10-medium-*-*-*-*-*-*-*-*-*-*-*" },
@@ -91,6 +92,7 @@ SymbolFont symbol_fonts[] = {
 	{ CMEX_FAMILY,  "cmex10"},
 	{ MSA_FAMILY,   "msam10"},
 	{ MSB_FAMILY,   "msbm10"},
+	{ DS_FAMILY,    "dsrom10"},
 	{ EUFRAK_FAMILY,"eufm10"},
 	{ RSFS_FAMILY,  "rsfs10"},
 	{ STMARY_FAMILY,"stmary10"},

src/mathed/InsetMathFont.cpp

@@ -134,6 +134,8 @@ void InsetMathFont::validate(LaTeXFeatures & features) const
 			features.require("tipa");
 		if (fontname == "ce" || fontname == "cf")
 			features.require("mhchem");
+		if (fontname == "mathds")
+			features.require("dsfont");
 	} else if (features.runparams().math_flavor == OutputParams::MathAsHTML) {
 		features.addCSSSnippet(
 			"span.normal{font: normal normal normal inherit serif;}\n"
@@ -163,9 +165,11 @@ void InsetMathFont::htmlize(HtmlStream & os) const
 		variant = "normal";
 	else if (tag == "frak" || tag == "mathfrak")
 		variant = "fraktur";
-	else if (tag == "mathbb" || tag == "mathbf"
+	else if (tag == "mathbf" || tag == "textbf")
-	         || tag == "textbf")
 		variant = "bold";
+	else if (tag == "mathbb" || tag == "mathbbm"
+	         || tag == "mathds")
+		variant = "double-struck";
 	else if (tag == "mathcal")
 		variant = "script";
 	else if (tag == "mathit" || tag == "textsl"
@@ -220,7 +224,7 @@ void InsetMathFont::mathmlize(MathStream & os) const
 	// no support at present for textipa, textsc, noun
 
 	if (!variant.empty()) {
-		if (tag == "mathbb") {
+		if (tag == "mathbb" || tag == "mathds") {
 			os << MTag("mstyle", "class='mathbb' mathvariant='" + variant + "'")
 			   << cell(0)
 			   << ETag("mstyle");

src/mathed/MathFactory.cpp

@@ -272,6 +272,8 @@ void initSymbols()
 					tmp.required = "wasysym";
 				else if (tmp.inset == "mathscr")
 					tmp.required = "mathrsfs";
+				else if (tmp.inset == "mathds")
+					tmp.required = "dsfont";
 			}
 
 			// symbol font is not available sometimes

src/mathed/MathSupport.cpp

@@ -775,6 +775,8 @@ fontinfo fontinfos[] = {
 			  inh_shape, Color_math},
 	{"mathbb",        MSB_FAMILY, inh_series,
 			  inh_shape, Color_math},
+	{"mathds",        DS_FAMILY, inh_series,
+			  inh_shape, Color_math},
 	{"mathtt",        TYPEWRITER_FAMILY, inh_series,
 			  inh_shape, Color_math},
 	{"mathit",        inh_family, inh_series,