Support "\" in non-wildcard exclusion entries

Support "\" in non-wildcard exclusion entries

"\" was treated differently in exclude rules depending on whether a
wildcard match was done. For wildcard rules, "\" was de-escaped in
fnmatch, but this was not done for other rules since they used strcmp
instead.  A file named "#foo" would not be excluded by "\#foo", but would
be excluded by "\#foo*".

We now treat all rules with "\" as wildcard rules.

Another solution could be to de-escape all non-wildcard rules as we
read them, but we would have to do the de-escaping exactly as fnmatch
does it to avoid inconsistencies.

Signed-off-by: Finn Arne Gangstad <finnag@pvv.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>