revlog: return lazy set from findcommonmissing
When computing the commonmissing, it greedily computes the entire set
immediately. On a large repo where the majority of history is irrelevant, this
causes a significant slow down.
Replacing it with a lazy set makes amend go from 11 seconds to 8.7 seconds.
#if unix-permissions no-root
$ hg init a
$ echo a > a/a
$ hg -R a ci -A -m a
adding a
$ hg clone a b
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo b > b/b
$ hg -R b ci -A -m b
adding b
$ chmod 100 a/.hg/store
$ hg -R b push a
pushing to a
abort: could not lock repository a: Permission denied
[255]
$ chmod 700 a/.hg/store
#endif