FindAdv: If possible use unicode instead of math command when searching

Wrong behaviour before this commit:
Open new lyx-file
insert
	unicode-insert 0x025c 0x1d08
Open adv-find dialog
search for unicode 0x025c OK
search for unicode 0x1d08 OK
search with regex for unicode 0x025c OK
search with regex for unicode 0x1d08 ==> NOT OK (because we are searching for \textrevepsilon
	and this was mapped to 0x025c

src/lyxfind.cpp

@@ -917,7 +917,7 @@ string escape_for_regex(string s, bool withformat)
 			if (lastpos == s.size())
 				break;
 		}
-		size_t end_pos = s.find("\\endregexp{}}", regex_pos + 8);
+		size_t end_pos = s.find("\\endregexp{", regex_pos + 8);
 		result += correctRegex(s.substr(regex_pos + 8, end_pos -(regex_pos + 8)), withformat);
 		lastpos = end_pos + 13;
 	}
@@ -3519,6 +3519,7 @@ MatchStringAdv::MatchStringAdv(lyx::Buffer & buf, FindAndReplaceOptions & opt)
 		string lead_as_regexp;
 		if (lead_size > 0) {
 			lead_as_regexp = string2regex(par_as_string.substr(0, lead_size));
+			(void)regex_replace(par_as_string_nolead, par_as_string_nolead, "\\$$", "");
 			(void)regex_replace(par_as_string_nolead, par_as_string_nolead, "}$", "");
 			par_as_string = par_as_string_nolead;
 			LYXERR(Debug::FIND, "lead_as_regexp is '" << lead_as_regexp << "'");

src/mathed/InsetMathHull.cpp

@@ -2357,12 +2357,19 @@ int InsetMathHull::plaintext(odocstringstream & os,
 	odocstringstream oss;
 	otexrowstream ots(oss);
 	Encoding const * const enc = encodings.fromLyXName("utf8");
-	TeXMathStream wi(ots, false, true, TeXMathStream::wsDefault, enc);
 
+	TeXMathStream::OutputType ot;
+	if (op.for_searchAdv == OutputParams::NoSearch)
+		ot = TeXMathStream::wsDefault;
+	else
+		ot = TeXMathStream::wsSearchAdv;
 	// Fix Bug #6139
-	if (type_ == hullRegexp)
+	if (type_ == hullRegexp) {
+		TeXMathStream wi(ots, false, true, ot, enc);
 		write(wi);
+	}
 	else {
+		TeXMathStream wi(ots, false, true, ot, enc);
 		for (row_type r = 0; r < nrows(); ++r) {
 			for (col_type c = 0; c < ncols(); ++c)
 				wi << (c == 0 ? "" : "\t") << cell(index(r, c));

src/mathed/InsetMathNest.cpp

@@ -358,8 +358,14 @@ void InsetMathNest::normalize(NormalStream & os) const
 
 void InsetMathNest::latex(otexstream & os, OutputParams const & runparams) const
 {
-	TeXMathStream wi(os, runparams.moving_arg, true,
+	TeXMathStream::OutputType ot;
-	                 runparams.dryrun ? TeXMathStream::wsDryrun : TeXMathStream::wsDefault,
+	if (runparams.for_searchAdv != OutputParams::NoSearch)
+		ot = TeXMathStream::wsSearchAdv;
+	else if (runparams.dryrun)
+		ot = TeXMathStream::wsDryrun;
+	else
+		ot = TeXMathStream::wsDefault;
+	TeXMathStream wi(os, runparams.moving_arg, true, ot,
 	                 runparams.encoding);
 	wi.strikeoutMath(runparams.inDeletedInset);
 	if (runparams.inulemcmd) {

src/mathed/MathExtern.cpp

@@ -1425,6 +1425,10 @@ void writeString(docstring const & s, TeXMathStream & os)
 		os << (os.asciiOnly() ? escape(s) : s);
 		return;
 	}
+	else if (os.output() == TeXMathStream::wsSearchAdv) {
+		os << s;
+		return;
+	}
 
 	if (os.lockedMode()) {
 		bool space;

src/mathed/MathStream.h

@@ -38,7 +38,8 @@ public:
 	enum OutputType {
 		wsDefault,
 		wsDryrun,
-		wsPreview
+		wsPreview,
+		wsSearchAdv
 	};
 	///
 	enum UlemCmdType {