Verify indentation was preserved before accepting a state as identical

This should prevent problems with parts of the document having a 'corrupt'
state when quickly scrolling down a big document.

Author: marijnh

lib/codemirror.js

@@ -1608,7 +1608,8 @@ var CodeMirror = (function() {
             if (hadState && compare(hadState, state)) return true;
           } else {
             if (changed !== false || !hadState) unchanged = 0;
-            else if (++unchanged > 3) return true;
+            else if (++unchanged > 3 && (!mode.indent || mode.indent(hadState, "") == mode.indent(state, "")))
+              return true;
           }
           ++i;
         });