git-apply: do not fix whitespaces on context lines.

git-apply: do not fix whitespaces on context lines.

Internal function apply_line() is called to copy both context lines
and added lines to the output buffer, while possibly fixing the
whitespace breakages depending on --whitespace=strip settings.
However, it did its fix-up on both context lines and added lines.

This resulted in two symptoms:

 (1) The number of lines reported to have been fixed up included
     these context lines.

 (2) However, the lines actually shown were limited to the added
     lines that had whitespace breakages.

Signed-off-by: Junio C Hamano <junkio@cox.net>