check_cr(): accept filenames with spaces in them (snippets, 710f111)

The check_cr() function was misbehaving when the input files contained spaces in their names. This commit spawns a subshell so as to conveniently do a temporary override of the IFS (Internal Field Separator).

Now the check_cr() function will accept filenames with spaces (or even tabs) in their names. It will not handle filenames with linefeeds in them, but this should not be a very common case.

Signed-off-by: Greg Hurrell <greg@hurrell.net>