obsolete: skip 'changectx' usage in unstable computation
We simplify the unstable computation code, skipping the expensive creation of
changectx object. We focus on efficient set operation and revnumber centric
functions.
In my mercurial development repository, this provides a 3x speedup to the
function:
before: 5.319 ms
after: 1.844 ms
repo details:
total changesets: 40886
obsolete changesets: 7756
mutable (not obsolete): 293
unstable: 30
running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: None
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: None