bug#11386: C++11 support: C++ mode gets (temporarily) confused by edits to convert "> >" to ">>" in templates

[James Dennett]

C++ mode gets confused if C++98 code is updated to omit the (now
unnecessary) space between the closing ">" angle brackets in template
argument lists.

To reproduce:

Start by typing the following (C++98) code:

int foo() {
  vector<vector<string> > temp;
}

So far, so good. Now go back and remove the extra space between the
closing angle brackets.  This will cause the closing } to not match
the opening { (according to emacs), so if you then add another
function below foo, you'll get something like:

int foo() {
  vector<vector<string>> temp;
  return 0;
}

      int bar() {
  }

where the indentation of everything after the function foo() is
broken.  Matching of the angle brackets is also broken.

The buffer can be restored to a good state by erasing and retyping the
inner "<" in the type.  Adding the extra space and removing it will
put the buffer back in a bad state.  Reading the code from file (with
or without the extra space) also leaves the buffer in a good state.