Skip "abort if high color set" logic for snapshots

Before, snapshots wouldn't work right for high color schemes, since
CSApproxImpl aborted early when a high color was found.  If the user
wanted this, though, they wouldn't have called CSApproxSnapshot.  So,
skip this logic in that case.

plugin/CSApprox.vim

@@ -688,6 +688,9 @@ function! s:CSApproxImpl()
   " sure that no groups are set to a value above 256, unless the color they're
   " set to can be set internally by vim (gotten by scraping
   " color_numbers_{88,256} in syntax.c:do_highlight)
+  "
+  " XXX: s:inhibit_hicolor_test allows this test to be skipped for snapshots
+  if !exists("s:inhibit_hicolor_test") || !s:inhibit_hicolor_test
     for hlid in hinums
       let val = highlights[hlid]
       if   (    val.cterm.bg > 15
@@ -701,6 +704,7 @@ function! s:CSApproxImpl()
         return
       endif
     endfor
+  endif
 
   call s:FixupGuiInfo(highlights)
   call s:FixupCtermInfo(highlights)
@@ -747,6 +751,7 @@ function! s:CSApproxSnapshot(file, overwrite)
   endif
 
   let save_t_Co = &t_Co
+  let s:inhibit_hicolor_test = 1
 
   try
     let lines = []
@@ -788,6 +793,7 @@ function! s:CSApproxSnapshot(file, overwrite)
     call writefile(lines, file)
   finally
     let &t_Co = save_t_Co
+    unlet s:inhibit_hicolor_test
   endtry
 endfunction