Fix issue with slow cursor moving in Python

This happened when moving the cursor in normal mode. The problem was that we
were calling SyntasticCheck on every cursor move because YCM would think that
the FileReadyToParse event processing returned diagnostics... but YCM only
integrates with Syntastic for C-family files.

Fixed by only triggering SyntasticCheck in C-family files.

autoload/youcompleteme.vim

@@ -29,6 +29,14 @@ let s:cursor_moved = 0
 let s:moved_vertically_in_insert_mode = 0
 let s:previous_num_chars_on_current_line = -1
 
+let s:forced_syntastic_checker_for = {
+      \ 'cpp': 1,
+      \ 'c': 1,
+      \ 'objc': 1,
+      \ 'objcpp': 1,
+      \ }
+
+
 function! youcompleteme#Enable()
   " When vim is in diff mode, don't run
   if &diff
@@ -165,6 +173,12 @@ function! s:ForceSyntasticCFamilyChecker()
 endfunction
 
 
+function! s:ForcedAsSyntasticCheckerForCurrentFiletype()
+  return g:ycm_register_as_syntastic_checker &&
+         \ get( s:forced_syntastic_checker_for, &filetype, 0 )
+endfunction
+
+
 function! s:AllowedToCompleteInCurrentFile()
   if empty( &filetype ) || getbufvar(winbufnr(winnr()), "&buftype") ==# 'nofile'
     return 0
@@ -411,7 +425,7 @@ endfunction
 function! s:UpdateDiagnosticNotifications()
   let should_display_diagnostics =
         \ get( g:, 'loaded_syntastic_plugin', 0 ) &&
-        \ g:ycm_register_as_syntastic_checker &&
+        \ s:ForcedAsSyntasticCheckerForCurrentFiletype() &&
         \ pyeval( 'ycm_state.NativeFiletypeCompletionUsable()' )
 
   if !should_display_diagnostics