Fix truncation

When the message is exactly as wide as the vim window, vim still
displays "press enter..." message.

Wen we want to avoid that we need to cut the message one character
shorter.

python/ycm/vimsupport.py

@@ -464,7 +464,7 @@ def PostVimMessage( message, warning = True, truncate = False ):
     vim_width = GetIntValue( '&columns' )
 
     message = message.replace( '\n', ' ' )
-    if len( message ) > vim_width:
+    if len( message ) >= vim_width:
       message = message[ : vim_width - 4 ] + '...'
 
     old_ruler = GetIntValue( '&ruler' )