util.url: copy urllib.unquote() into util to improve startup times
The ui class uses util.hasscheme() in a couple of places, causing hg
to import urllib even when it doesn't need to. This copies
urllib.unquote() to avoid that import.
perfstartup time before the URL refactoring (8796fb6af67e):
! wall 0.050692 comb 0.000000 user 0.000000 sys 0.000000 (best of 100)
before this change:
! wall 0.064742 comb 0.000000 user 0.000000 sys 0.000000 (best of 100)
after this change:
! wall 0.052126 comb 0.000000 user 0.000000 sys 0.000000 (best of 100