contrib/vimrc: detect more C-like files

contrib/vimrc: detect more C-like files

Currently this script doesn't set the indentation style for the standard
library headers under libstdc++/ because they lack a file extension.
But they do have a modeline, so the file type is still set appropriately
by Vim.  So by inspecting &filetype, we can also detect these standard
library headers as C-like files.

contrib/ChangeLog:

	* vimrc (SetStyle): Also inspect &filetype to determine whether
	a file is C-like.