git-quiltimport.sh: allow declining fuzz with --exact option

git-quiltimport unconditionally passes "-C1" to "git apply",
supposedly to roughly match the quilt default of --fuzz 2.  Allow
users to pass --exact option to disable it, requiring the patch to
apply without any fuzz.

Also note that -C1 and fuzz=2 is not identical.  Most patches have
three lines of context, so fuzz=2 leaves one relevant line of
context.  But for any patches with more or less context this is not
true.  git-apply has no option for fuzz, so any emulation will
always be best-effort.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
git-quiltimport: flip the default not to allow fuzz

Trying to be as strict as possible when applying the patch may be a
good discipline, so let's flip the default but we can be helpful to
those who do rely on the original behaviour thanks to the previous
change to add -C$n option.

Suggest using -C1 when (and only when):

 - "git apply" without fuzz fails to apply; and
 - the user did not specify a -C$n or --exact option; and
 - "git apply -C1" (old behaviour) would have succeeded.

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