packagescan: handle demandload module naming changes.

Update configuration note with mercurial.ini change from Thomas

fix parsing of tags. make parse errors useful. add new tag tests. old code read every head of .hgtags. delete and recreate of .hgtags gave new head, but if error in deleted rev, .hgtags had error messages every time it was parsed. this was very hard to fix, because deleted revs hard to get back and update, needed merges too. new code reads .hgtags on every head. advantage is if parse error happens with new code, is possible to fix them by editing .hgtags on a head and committing. NOTE: new code uses binary search of manifest of each head to be fast, but still much slower than old code. best thing would be to have delete record stored in filelog so we never touch manifest. could find live heads directly from filelog. this is more work than i want now. new tests check for parse of tags on different heads, and inaccessible heads created by delete and recreate of .hgtags.

test-globalopts: make sed expression better.

If HOME is defined on Windows, Mercurial uses it. Document this.

merge emacs patches.

Emacs: separate limitations of revision range and shown changesets. For revision range limitation, use "-r" opt with range notation at "hg log" invocation, and use hg-rev-completion-limit as default value. For shown changesets limitation, use "-l" opt at "hg log" invocation, and use hg-log-limit as default value.

Emacs: adapt read-file-name invocation for (non-X)Emacs 21.4. this patch deters hg-read-file-name from passing hg-file-history to read-file-name as 6th parameter in non-X Emacs environment.