Fallback to using git ls-files if ag is missing

vim/settings/ctrlp.vim

@@ -4,6 +4,10 @@ if executable('ag')
 
   " ag is fast enough that CtrlP doesn't need to cache
   let g:ctrlp_use_caching = 0
+else
+  " Fall back to using git ls-files if Ag is not available
+  let g:ctrlp_custom_ignore = '\.git$\|\.hg$\|\.svn$'
+  let g:ctrlp_user_command = ['.git', 'cd %s && git ls-files . --cached --exclude-standard --others']
 endif
 
 " Default to filename searches - so that appctrl will find application