Fix undo of entering \hline

It was broken with 6d75800f5d as noticed by Enrico. The fix is to use undo
groups (thanks Jean-Marc).

src/Cursor.cpp

@@ -1599,8 +1599,11 @@ bool Cursor::macroModeClose()
 
 	docstring const name = s.substr(1);
 	InsetMathNest * const in = inset().asInsetMath()->asNestInset();
-	if (in && in->interpretString(*this, s))
+	if (in && in->interpretString(*this, s)) {
+		// end undo group that was opened before in was created
+		endUndoGroup();
 		return true;
+	}
 	MathAtom atom = buffer()->getMacro(name, *this, false) ?
 		MathAtom(new MathMacro(buffer(), name)) : createInsetMath(name, buffer());
 
@@ -1634,6 +1637,8 @@ bool Cursor::macroModeClose()
 			insert(selection);
 	}
 
+	// end undo group that was opened before in was created
+	endUndoGroup();
 	return true;
 }
 

src/mathed/InsetMathGrid.cpp

@@ -184,6 +184,7 @@ bool InsetMathGrid::interpretString(Cursor & cur, docstring const & str)
 		FuncStatus status;
 		if (getStatus(cur, fr, status)) {
 			if (status.enabled()) {
+				cur.recordUndoInset();
 				rowinfo_[cur.row()].lines_++;
 				return true;
 			}

src/mathed/InsetMathNest.cpp

@@ -848,10 +848,14 @@ void InsetMathNest::doDispatch(Cursor & cur, FuncRequest & cmd)
 
 	case LFUN_SELF_INSERT:
 		if (cmd.argument().size() != 1) {
+			// use a group because interpretString() might
+			// record an extra undo step
+			cur.beginUndoGroup();
 			cur.recordUndoSelection();
 			docstring const arg = cmd.argument();
 			if (!interpretString(cur, arg))
 				cur.insert(arg);
+			cur.endUndoGroup();
 			break;
 		}
 		// Don't record undo steps if we are in macro mode and thus
@@ -1663,6 +1667,8 @@ bool InsetMathNest::interpretChar(Cursor & cur, char_type const c)
 				cur.cell().erase(cur.pos());
 				cur.plainInsert(MathAtom(
 					new InsetMathBig(name.substr(1), delim)));
+				// end undo group that was opened before p was created
+				cur.endUndoGroup();
 				return true;
 			}
 		}
@@ -1706,9 +1712,12 @@ bool InsetMathNest::interpretChar(Cursor & cur, char_type const c)
 		bool reduced = cap::reduceSelectionToOneCell(cur);
 		if (reduced || !cur.selection()) {
 			docstring const safe = cap::grabAndEraseSelection(cur);
-			if (!cur.inRegexped())
+			if (!cur.inRegexped()) {
+				// open a group because interpretString() might
+				// record an extra undo step when finalizing
+				cur.beginUndoGroup();
 				cur.insert(MathAtom(new InsetMathUnknown(from_ascii("\\"), safe, false)));
-			else
+			} else
 				cur.niceInsert(createInsetMath("backslash", buf));
 		}
 		return true;

src/mathed/MathData.cpp

@@ -28,8 +28,6 @@
 #include "CoordCache.h"
 #include "Cursor.h"
 
-#include "mathed/InsetMathUnknown.h"
-
 #include "support/debug.h"
 #include "support/docstream.h"