OS X: try cheap ascii .lower() in normcase before making full unicode dance
This is similar to what is done in encoding.lower, introduced in c481761033bd.
This has been seen making 'hg up' and 'hg st' in a 50000+ files repo 13%
faster.
This might make Mercurial slightly slower for users who mainly use non-ASCII
filenames. That is a reasonable trade-off.
os = <unloaded module 'os'>
os.system = <built-in function system>
os = <module 'os' from '?'>
util = <unloaded module 'util'>
util.system = <function system at 0x?>
util = <module 'mercurial.util' from '?'>
util.system = <function system at 0x?>
fred = <unloaded module 're'>
re = <unloaded module 'sys'>
fred = <unloaded module 're'>
fred.sub = <function sub at 0x?>
fred = <proxied module 're'>
re = <unloaded module 'sys'>
re.stderr = <open file '<whatever>', mode 'w' at 0x?>
re = <proxied module 'sys'>