[PATCH 00 of 13 RFC] consistent and more reliable URL parsing (part 2)

[Brodie Rao]

Here's an updated patch series addressing some of the issues brought
up during the discussion.

Changes include:

- A fix Python 2.4 test failures involving URLs without trailing
  slashes.

- Patches that let schemes override drive letter detection when it
  makes sense and has no impact.

- A hack to preserve compatibility with bundle URLs. The parser no
  longer considers bundle URLs to have hostnames (and it doesn't try
  to URL decode them either).

- More examples in the behavior table of the last patch's commit
  message.

All existing parsing behavior is now preserved, though there are two
minor output changes:

- bundle://... URLs are always printed as bundle:... in UI messages.

- URLs like http://localhost:80 are printed as http://localhost:80/ in
  UI messages.

And one patch that I've added that might constitute a backwards
compatibility concern:

- file:// URLs containing host names other than localhost, 127.0.0.1,
  or [::1] now cause hg to abort with a friendly error message.