dirstate: cache util.normcase while constructing the foldmap This is a small win on OS X. hg perfdirstatefoldmap: before: wall 0.399708 comb 0.410000 user 0.390000 sys 0.020000 (best of 25) after: wall 0.386331 comb 0.390000 user 0.370000 sys 0.020000 (best of 25)

normcase: for darwin, use fast ASCII lower Constructing the foldmap is much faster on OS X now. For a large real-world repo, hg perfdirstatefoldmap: before: wall 0.805278 comb 0.800000 user 0.790000 sys 0.010000 (best of 13) after: wall 0.399708 comb 0.410000 user 0.390000 sys 0.020000 (best of 25) This is a nice boost to 'hg status', especially with the third-party hgwatchman extension enabled (which eliminates stat calls). For the above repo, 'hg status' goes from 1.17 seconds to 0.74.

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.