strip: remove -b/--backup codepaths cset ba3bc6474bbf has removed this option. This commit just tidies the code that was associated to it. It also fixes the internal calls to the strip() function. Before this change, any function that thought it would want as a final safety to keep a partial backup bundle (bundling changes not linearly related to the current change being stripped), had to explicitly pass a backup="strip" option. With this change, these backups are always kept in case of an exception and always removed if there is no exception. Only full backups can be specified with backup=True or no full backups with backup=False.

simplemerge: remove dead code The following functions in simplemerge are dead code. I reran "make test-merge*" after this change, and it passed. Looks like cruft that we've been carrying since we nabbed this code from bzr.

basectx: add missing, merge, and branch args to dirty method This fixes a discrepency for basectx and classes that inherit from it. Now callers can pass these arguments to any context without an exception being raised.

basefilectx: move isexec and islink from memfilectx This will be used in the future for creating memctx objects from other store-type objects, such as a patch store or even another context.

tests: fix pyflakes test whitespace breakage

pushkey: wrap pushkey phase movement in a transaction Phases are not yet inside the transaction, but we need to prepare for it. So we wrap the phase movement inside a transaction.