changegroup: store old heads as a set Previously, the "oldheads" variable was a list. On a repository at Mozilla with 46,492 heads, profiling revealed that list membership testing was dominating execution time of applying small changegroups. This patch converts the list of old heads to a set. This makes membership testing significantly faster. On the aforementioned repository with 46,492 heads: $ hg unbundle <file with 1 changeset> before: 18.535s wall after: 1.303s Consumers of this variable only check for truthiness (`if oldheads`), length (`len(oldheads)`), and (most importantly) item membership (`h not in oldheads` - which occurs twice). So, the change to a set should be safe and suitable for stable. The practical effect of this change is that changegroup application and related operations (like `hg push`) no longer exhibit an O(n^2) CPU explosion as the number of heads grows.

checkheads: extract obsolete post processing in its own function The checkheads function is long and complex, extract that logic in a subfunction is win in itself. As the comment in the code says, this postprocessing is currently very basic and either misbehave or fails to detect valid push in many cases. My deeper motive for this extraction is to be make it easier to provide extensive testing of this case and strategy to cover them. Final test and logic will makes it to core once done.

tests: make test-simplekeyvaluefile.py py2.6-compatible Python 2.6 unittest.TestCase does not have assertRaisesRegexp.