Whitespace breakages are checked while the patch is being parsed.
Disable them at the beginning of parse_chunk(), where each
individual patch is parsed, immediately after we learn the name of
the file the patch applies to and before we start parsing the diff
contained in the patch.

One may naively think that we should be able to not just skip the
whitespace checks but simply fast-forward to the next patch without
doing anything once use_patch() tells us that this patch is not
going to be used.  But in reality we cannot really skip much of the
parsing in order to do such a "fast-forward", primarily because
parsing "@@ -k,l +m,n @@" lines and counting the input lines is how
we determine the boundaries of individual patches.

Signed-off-by: Junio C Hamano <gitster@pobox.com>