Fix test scripts

'precommit.sh' will run 'runtime_tests.sh' instead of maintaining a copy
of the equivalent code itself.

'runtime_tests.sh' will pass any command-line arguments on to nosetests,
so that invocations like:
$ ./runtime_tests.sh --failed
are possible

Test Plan:
$ ./precommit.sh
$ ./runtime_tests.sh
$ ./runtime_tests.sh --failed
$ ./runtime_tests.sh --coverage
Arcyd: use new branch abstraction to simplify

The 'abdi_processrepo' module is bloated with branch-pair fiddling that
can be simplified by introducing a 'managed branch' abstraction which
manages the relationship between a review branch and it's paired
tracking branch.

Test Plan: $ ./precommit.sh
fixup! Arcyd: use new branch abstraction to simplify
fixup! Arcyd: use new branch abstraction to simplify