Check for local changes with "goto"

Check for local changes with "goto"

This is done by default, unless the --keep option is passed, for
consistency with the "pop" command. The index is checked in the
Transaction.run() function so that other commands could benefit from
this feature (off by default).

This behaviour can be overridden by setting the stgit.autokeep option.

Signed-off-by: Catalin Marinas <catalin.marinas@gmail.com>
Acked-by: Karl Hasselström <kha@treskal.com>