bundlerepo: make baserevision return raw text "baserevision" returns the text that will be used to apply deltas. Since deltas are against raw texts, "baserevision" should return raw text. Now test-flagprocessor.t points us to a new error.

test-flagprocessor: add tests about bundlerepo This shows flag processor is broken with a bundle repo. The test creates non-liner history to exercise code path where the deltaparent cannot be reused.

test-flagprocessor: use changegroup3 in bundle2 This will force "hg bundle" to use changegroup3 in the test. It is important since only changegroup3 preserves revlog flags.