subrepo: add basic support to hgsubrepo for the files command Paths into the subrepo are not yet supported. The need to use the workingctx in the subrepo will likely be used more in the future, with the proposed working directory revset symbol. It is also needed with archive, if that code is to be reused to support 'extdiff -S'. Unfortunately, it doesn't seem possible to put the smarts in subrepo.subrepo(), as it breaks various status and diff tests. I opted not to pass the desired revision into the subrepo method explicitly, because the only ones that do pass an explicit revision are methods like status and diff, which actually operate on two contexts- the subrepo state and the explicitly passed revision.

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'>
node = <module 'mercurial.node' from '?'>