dirstate: use a presized dict for the dirstate
This uses a simple heuristic to avoid expensive resizes.
On a real-world repo with around 400,000 files, perfdirstate:
before: ! wall 0.155562 comb 0.160000 user 0.150000 sys 0.010000 (best of 64)
after: ! wall 0.132638 comb 0.130000 user 0.120000 sys 0.010000 (best of 75)
On another real-world repo with around 250,000 files:
before: ! wall 0.098459 comb 0.100000 user 0.090000 sys 0.010000 (best of 100)
after: ! wall 0.089084 comb 0.090000 user 0.080000 sys 0.010000 (best of 100)
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present