Prevent tabs in error messages from causing "press enter" prompt.

Convert the tabs to spaces so that they are counted towards the window width
and the status message does not wrap.

plugin/syntastic.vim

@@ -439,7 +439,8 @@ function! s:WideMsg(msg)
     let old_ruler = &ruler
     let old_showcmd = &showcmd
 
-    let msg = strpart(a:msg, 0, winwidth(0)-1)
+    let msg = substitute(a:msg, "\t", repeat(" ", &tabstop), "g")
+    let msg = strpart(msg, 0, winwidth(0)-1)
 
     "This is here because it is possible for some error messages to begin with
     "\n which will cause a "press enter" prompt. I have noticed this in the