Bug fix: Don't highlight C tags inside #if 0 (issue #57)

$VIMRUNTIME/syntax/c.vim is a bit of a mess, I can't make heads or tails
of it :-). In my simple #if 0 / #if 1 / #else tests this fixes the issue,
but I'm not sure that there are no corner cases left.

See issue #57 on GitHub:
  #57

Author: xolox

autoload/xolox/easytags.vim

@@ -1,9 +1,9 @@
 " Vim script
 " Author: Peter Odding <peter@peterodding.com>
-" Last Change: May 25, 2013
+" Last Change: June 17, 2013
 " URL: http://peterodding.com/code/vim/easytags/
 
-let g:xolox#easytags#version = '3.3.6'
+let g:xolox#easytags#version = '3.3.7'
 
 " Public interface through (automatic) commands. {{{1