Minor cleanup.

plugin/syntastic.vim

@@ -9,7 +9,7 @@
 "
 "============================================================================
 
-if exists('g:loaded_syntastic_plugin')
+if exists('g:loaded_syntastic_plugin') || &compatible
     finish
 endif
 let g:loaded_syntastic_plugin = 1
@@ -19,11 +19,16 @@ if has('reltime')
     lockvar! g:_SYNTASTIC_START
 endif
 
-let g:_SYNTASTIC_VERSION = '3.6.0-123'
+let g:_SYNTASTIC_VERSION = '3.6.0-124'
 lockvar g:_SYNTASTIC_VERSION
 
 " Sanity checks {{{1
 
+if v:version < 700 || (v:version == 700 && !has('patch175'))
+    call syntastic#log#error('need Vim version 7.175 or later')
+    finish
+endif
+
 for s:feature in [
             \ 'autocmd',
             \ 'eval',
@@ -130,7 +135,7 @@ let s:_DEBUG_DUMP_OPTIONS = [
         \ 'shelltemp',
         \ 'shellxquote'
     \ ]
-if v:version > 703 || (v:version == 703 && has('patch446'))
+if exists('+shellxescape')
     call add(s:_DEBUG_DUMP_OPTIONS, 'shellxescape')
 endif
 lockvar! s:_DEBUG_DUMP_OPTIONS
@@ -231,12 +236,13 @@ endfunction " }}}2
 " Autocommands {{{1
 
 augroup syntastic
+    autocmd!
     autocmd BufReadPost  * call s:BufReadPostHook()
     autocmd BufWritePost * call s:BufWritePostHook()
     autocmd BufEnter     * call s:BufEnterHook()
 augroup END
 
-if v:version > 703 || (v:version == 703 && has('patch544'))
+if exists('##QuitPre')
     " QuitPre was added in Vim 7.3.544
     augroup syntastic
         autocmd QuitPre * call s:QuitPreHook()