completion: add a debugpathcomplete command The bash_completion code uses "hg status" to generate a list of possible completions for commands that operate on files in the working directory. In a large working directory, this can result in a single tab-completion being very slow (several seconds) as a result of checking the status of every file, even when there is no need to check status or no possible matches. The new debugpathcomplete command gains performance in a few simple ways: * Allow completion to operate on just a single directory. When used to complete the right commands, this considerably reduces the number of completions returned, at no loss in functionality. * Never check the status of files. For completions that really must know if a file is modified, it is faster to use status: hg status -nm 'glob:myprefix**' Performance: Here are the commands used by bash_completion to complete, run in the root of the mozilla-central working dir (~77,000 files) and another repo (~165,000 files): All "normal state" files (used by e.g. remove, revert): mozilla other status -nmcd 'glob:**' 1.77 4.10 sec debugpathcomplete -f -n 0.53 1.26 debugpathcomplete -n 0.17 0.41 ("-f" means "complete full paths", rather than the current directory) Tracked files matching "a": mozilla other status -nmcd 'glob:a**' 0.26 0.47 debugpathcomplete -f -n a 0.10 0.24 debugpathcomplete -n a 0.10 0.22 We should be able to further improve completion performance once the critbit work lands. Right now, our performance is limited by the need to iterate over all keys in the dirstate.