Fix bug where strings were not flattened before regexp.

src/api.cc

Index: src/api.cc
===================================================================
--- src/api.cc	(revision 1138)
+++ src/api.cc	(working copy)
@@ -2037,7 +2037,7 @@
   i::Handle<i::String> str = Utils::OpenHandle(this);
   // Flatten the string for efficiency.  This applies whether we are
   // using StringInputBuffer or Get(i) to access the characters.
-  str->TryFlatten(i::StringShape(*str));
+  str->TryFlattenIfNotFlat(i::StringShape(*str));
   int end = length;
   if ( (length == -1) || (length > str->length() - start) )
     end = str->length() - start;
@@ -2062,7 +2062,7 @@
   i::Handle<i::String> str = Utils::OpenHandle(this);
   // Flatten the string for efficiency.  This applies whether we are
   // using StringInputBuffer or Get(i) to access the characters.
-  str->TryFlatten(i::StringShape(*str));
+  str->TryFlattenIfNotFlat(i::StringShape(*str));
   int end = length;
   if ( (length == -1) || (length > str->length() - start) )
     end = str->length() - start;