FindAdv: Simplify search for chars '&', '%', '#' and '_'

This is not possible for '$', because of the latex-meaning to
start/end math inset.
Therefore, if not ignoring format, we still have to use
[\\][\$] in regex in order to find '$' in text.

src/Paragraph.cpp

@@ -1297,9 +1297,17 @@ void Paragraph::Private::latexSpecialChar(otexstream & os,
 		column += 14;
 		break;
 
-	case '$': case '&':
+	case '&':
-	case '%': case '#': case '{':
+	case '%': case '#':
-	case '}': case '_':
+	case '_':
+		if (runparams.for_search) {
+			os.put(c);
+			column += 1;
+			break;
+		}
+		// fall through
+	case '$':
+	case '{': case '}':
 		os << '\\';
 		os.put(c);
 		column += 1;

src/insets/InsetIndex.cpp

@@ -74,19 +74,19 @@ void InsetIndex::latex(otexstream & os, OutputParams const & runparams_in) const
 		os << '{';
 	}
 
-	odocstringstream ourplain;
+	odocstringstream ourlatex;
-	InsetText::plaintext(ourplain, runparams);
+	otexstream ots(ourlatex);
+	InsetText::latex(ots, runparams);
 	if (runparams.for_search) {
 		// No need for special handling, if we are only searching for some patterns
-		os << ourplain.str() << "}";
+		os << ourlatex.str() << "}";
 		return;
 	}
 	// get contents of InsetText as LaTeX and plaintext
-	odocstringstream ourlatex;
+	odocstringstream ourplain;
+	InsetText::plaintext(ourplain, runparams);
 	// FIXME: do Tex/Row correspondence (I don't currently understand what is
 	// being generated from latexstr below)
-	otexstream ots(ourlatex);
-	InsetText::latex(ots, runparams);
 	docstring latexstr = ourlatex.str();
 	docstring plainstr = ourplain.str();
 

src/lyxfind.cpp

@@ -1442,8 +1442,16 @@ void LatexInfo::buildEntries(bool isPatternString)
     if (key == "") {
       if (sub.str(0)[0] == '\\')
         key = sub.str(0)[1];
-      else
+      else {
         key = sub.str(0);
+        if (key == "$") {
+          size_t k_pos = sub.position(size_t(0));
+          if ((k_pos > 0) && (interval.par[k_pos - 1] == '\\')) {
+            // Escaped '$', ignoring
+            continue;
+          }
+        }
+      }
     };
     if (evaluatingRegexp) {
       if (sub.str(1).compare("endregexp") == 0) {