git-svn: support fetch with autocrlf on

git-svn: support fetch with autocrlf on

Before commit d3c9634e, performing a "git svn rebase" that fetched a
change containing CRLFs corrupted the git-svn meta-data. This was
worked around in d3c9634e by setting core.autocrlf to "false" in the
per-repo config when initing the clone. However, if the config
variable was later changed, the corruption would still occur.

This patch tries to fix it while allowing core.autocrlf to be
enabled, by disabling filters when when hashing.

git-svn is currently the only call-site for hash_and_insert_object
(apart from the test-suite), so changing it should be safe.

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Acked-by: Eric Wong <normalperson@yhbt.net>