Fix rm for older versions of dulwich.
Fix rm for older versions of dulwich.

On dulwich 0.9.4 (which is what Ubuntu 14.04 packages),
dulwich.porcelain.status() does not exist.  To make it
work there, we essentially copy that functionality out
of newer dulwich and maintain it locally.

Signed-off-by: Chris Lalancette <281cd07d7578d97c83271fbbf2faddb83ab3791c@irobot.com>

jake4679/git-got,manuelnaranjo/git-got