wildmatch: support "no FNM_PATHNAME" mode

wildmatch: support "no FNM_PATHNAME" mode

So far, wildmatch() has always honoured directory boundary and there
was no way to turn it off. Make it behave more like fnmatch() by
requiring all callers that want the FNM_PATHNAME behaviour to pass
that in the equivalent flag WM_PATHNAME. Callers that do not specify
WM_PATHNAME will get wildcards like ? and * in their patterns matched
against '/', just like not passing FNM_PATHNAME to fnmatch().

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>