perf: add a way to measure the perf of constructing the foldmap Constructing the foldmap is a necessary part of operations like 'hg status' on OS X. This command allows us to measure the perf of constructing it.

encoding.lower: use fast ASCII lower This benefits, among other things, the case collision auditor. On a Linux system with a large real-world repo where all filenames are ASCII, hg perfcca: before: wall 0.260157 comb 0.270000 user 0.230000 sys 0.040000 (best of 38) after: wall 0.164616 comb 0.160000 user 0.160000 sys 0.000000 (best of 54)