Also removed a superfluous test.
Signed-off-by: NAriel Badichi <abadichi@bezeqint.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When the specfile (export-subst) attribute was introduced, it added a
dependency from archive-{tar|zip}.c to builtin-archive.c. This broke the
support for archive-operations in libgit.a since builtin-archive.o doesn't
belong in libgit.a.

This patch moves the functions required by libgit.a from builtin-archive.c
to the new file archive.c (which becomes part of libgit.a).
Signed-off-by: NLars Hjemli <hjemli@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>