There is now only peer scheme lookup. Repository lookup goes through
peer scheme lookup. When peer and repo types are finally separated,
repo lookup will use peer.local() to get a repository object.
The underbar is dropped so that extensions can patch the table.
The introduction of the new URL parsing code has created a startup
time regression. This is mainly due to the use of url.hasscheme() in
the ui class. It ends up importing many libraries that the url module
requires.
This fix helps marginally, but if we can get rid of the urllib import
in the URL parser all together, startup time will go back to normal.
perfstartup time before the URL refactoring (707e4b1e8064):
! wall 0.050692 comb 0.000000 user 0.000000 sys 0.000000 (best of 100)
current startup time (9ad1dce9e7f4):
! wall 0.070685 comb 0.000000 user 0.000000 sys 0.000000 (best of 100)
after this change:
! wall 0.064667 comb 0.000000 user 0.000000 sys 0.000000 (best of 100)
To allow one letter schemes, this makes the extension override
url.has_drive_letter() to return False for any schemes defined.
On Windows, the extension will raise util.Abort for any schemes that
conflict with existing drive letters.
