fix -I/-X when relative paths used or in subdir

hg.repository: many routines expect path to be a string even if empty.

fix bug in localrepo.changes. caused by 1e32e2fe8a677c391049d40b8794478976a0a914.

use commit time as mtime for file archives. now output from two run of "hg archive -t zip" is same.

archive: make "hg archive -t XXX -" to write to stdout

merge with crew.

Fix cold cache diff performance cold cache diff performance has regressed in two ways. localrepo.changes has optimizations for diffing against the working dir parent that expect node1 to be None. commands.revpair() usage means that commands.dodiff() never sends node1 == None. This is fixed in localrepo.changes by checking against the dirstate parents. In the non-dirstate parents case, localrepo.changes does a loop comparing files without first sorting the file names, leading to random access across the disk.