Add tests for commit, reuse master branch transport.
* bzrlib/workingtree.py: (WorkingTree.pull): Add a possible_transports parameter, forward it to branch.pull.
* bzrlib/branch.py: (Branch.pull, BzrBranch.pull, BzrBranch5.pull): Add a possible_transports parameter. (BzrBranch5.pull): Make master branch transport added to possible_transports
* bzrlib/tests/commands/test_commit.py: New file testing against multiple connections during commit.
* bzrlib/builtins.py: (cmd_pull.run): Allows master branch transports to be reused. (cmd_commit): 'fixes' is a ListOption, its default value should be [].
* bzrlib/tests/commands/test_pull.py: Fix import statements. (TestPull.test_pull_with_bound_branch): New test.