revlog: fix _cache usage in revision() As documented at revlog.__init__, revlog._cache stores raw text. The current read and write usage of "_cache" in revlog.revision lacks of raw=True check. This patch fixes that by adding check about raw, and storing rawtext explicitly in _cache. Note: it may slow down cache hit code path when raw=False and flags=0. That performance issue will be fixed in a later patch. test-revlog-raw now points us to a new problem.

revlog: rename some "text"s to "rawtext" This makes code easier to understand. "_addrevision" is left untouched - it will be changed in a later patch.

revlog: clarify flagprocessor documentation The words "text", "newtext", "bool" could be confusing. Use explicit "text" or "rawtext" and document more about the "bool".

revlog: add a stronger test for raw processing There are some issues about revlog raw processing (flag processor). The test is relatively strong covering many cases. It will verify fixes.