Fixed highlighting for -- and ++

CHANGES.txt

       "python_highlight_string_templates" option;
     - Added support for str.format syntax controlled by
       "python_highlight_string_format" option;
+    - Removed highlighting for "--" and "++" because it's a valid Python
+      expressions which can be interpreted as "a + +b";
 
 Revision 2.5.6 (2007-02-04):
 

python.vim

 " Errors
 syn match pythonError		"\<\d\+\D\+\>" display
 syn match pythonError		"[$?]" display
-syn match pythonError		"[-+&|]\{2,}" display
+syn match pythonError		"[&|]\{2,}" display
 syn match pythonError		"[=]\{3,}" display
 
 " TODO: Mixing spaces and tabs also may be used for pretty formatting multiline