simplestore: correctly implement flag processors There were a couple of bugs around the implementation of flags processing with the simple store. After these changes, test-flagprocessor.t now passes! test-flagprocessor.t was also updated to include explicit test coverage that pushed data is as expected on the server. The test extension used by test-flagprocessor.t has been updated so it monkeypatches the object returned from repo.file() instead of monkeypatching filelog.filelog. This allows it to work with extensions that return custom types from repo.file(). The monkeypatching is rather hacky and probably is performance prohibitive for real repos. We should probably come up with a better mechanism for registering flag processors so monkeypatching isn't needed. Differential Revision: https://phab.mercurial-scm.org/D3116