Replace 'unlink' with 'rm' in tests.

Several Unix-like systems (eg. OpenBSD) don't have 'unlink' utility. 'rm' does
exactly the same job, so using 'rm' instead of 'unlink' makes dulwich tests
more portable.

Signed-off-by: Jelmer Vernooij <jelmer@samba.org>
Update NEWS.
Support creating unannotated tags.
Add objectish argument to porcelain.tag.
Add time and timezone arguments for tag.
Support str timezones.
Add bin/dulwich support for reset command.
Sort command names in bin/dulwich.
Drop support for Python < 2.7.
No longer build for Python 2.6.
Fix reset handling in fastexport module.
Add bug #
Support http.proxy setting in HttpGitClient.
Add support for 'http.useragent'.
Upload pack: We have to wait for the client to close the connection by itself.

Most versions of Git freakout if we close the connection ourselves,
and will not create an empty repository on clone.
Test for ProtocolGraphWalker if the repository is empty.
Update NEWS.
Apply lib2to3.fixes.fix_except
Apply lib2to3.fixes.fix_numliterals
Change relative imports to absolute.