Extended test case to test dirstate length bug fixed in a7e95e3606c7.

Use length of file instead of length of change for the dirstate entry.

Fix 3-way-merge of original parent, workdir and new parent. The dirstate has to match what is in the repository (what would be checked out with 'hg update -C'), because the resulting file may be identical to the new parent, or it may be completely different. Previously the dirstate wasn't updated, so if you changed the file to look like the original parent, it might be considered unmodified relative to the new parent.

dirstate.changes() now distinguishes 'hg remove'd or just deleted files. Interface is not yet changed. Non-regular files are considered to be removed or deleted. Removed the unneeded match(fn) call for adding to the unknown list.

Use correct term "closed interval" for ranges.

Trap OSError when deleting env vars On the other OS, it seems that case insensitivity for environment vars can bite users when using some unknown combination of python 2.4.1 and win2kSP4+minsys (and probably other vversions of these softwares). The best way to avoid problems in those weird cases is to ignore OSError exception during env var deletion.