A change in RBTools 3.1 resulted in a duplicate with_errors= argument

passed to execute() in apply_patch(). MercurialClient._execute()

was explicitly setting this and also allowing any arbitrary **kwargs

to be passed in. This was missed due to lack of unit testing.
This changes _execute() to take in with_errors as an argument with

the default we want to set. It also adds unit testing for

apply_patch() to ensure this code path does not regress.

Unit tests pass.
Tested by a customer that hit this issue.