Handle \textgreek commands from unicodesymbols

This is the second part of bug #8553: The symbols defined in unicodesymbols
are now detected correctly and converted to unicode, so no ERT anymore.

src/tex2lyx/test/box-color-size-space-align.lyx.lyx

@@ -2120,39 +2120,7 @@ from textcomp: №™
 \begin_layout Standard
 
 \size normal
-from textgreek and textcyr: 
-\begin_inset ERT
-status collapsed
-
-\begin_layout Plain Layout
-
-\backslash
-textgreek
-\end_layout
-
-\end_inset
-
-
-\begin_inset ERT
-status collapsed
-
-\begin_layout Plain Layout
-{
-\end_layout
-
-\end_inset
-
->a
-\begin_inset ERT
-status collapsed
-
-\begin_layout Plain Layout
-}
-\end_layout
-
-\end_inset
-
-в
+from textgreek and textcyr: ἀв
 \end_layout
 
 \begin_layout Standard

src/tex2lyx/text.cpp

@@ -4552,8 +4552,9 @@ void parse_text(Parser & p, ostream & os, unsigned flags, bool outer,
 			// Only use text mode commands, since we are in text mode here,
 			// and math commands may be invalid (bug 6797)
 			string name = t.asInput();
-			// handle the dingbats and Cyrillic
-			if (name == "\\ding" || name == "\\textcyr")
+			// handle the dingbats, cyrillic and greek
+			if (name == "\\ding" || name == "\\textcyr" ||
+			    (name == "\\textgreek" && !preamble.usePolyglossia()))
 				name = name + '{' + p.getArg('{', '}') + '}';
 			// handle the ifsym characters
 			else if (name == "\\textifsymbol") {