After chdir to run grep, return to old directory

Signed-off-by: David Turner <dturner@twitter.com>
Optionally use VMAC for index integrity checking

Using SHA-1 to check the index integrity takes up about 5% of the
runtime of git status (depending on the repository). We can do better
by using VMAC instead.  VMAC isn't really intended for integrity
checking, but it has the correct properties.  It is also approximately
5 times faster than SHA-1 on my machine.

Signed-off-by: David Turner <dturner@twitter.com>
Watchman support

Add support for filesystem view caching and updating via Facebook's
Watchman daemon.

Signed-off-by: David Turner <dturner@twitter.com>
hashmap: Remove unused functions

Remove str(i?)hash functions from hashmap.c as they are unused

Signed-off-by: David Turner <dturner@twitter.com>