revset: fix ancestors(null) to include null revision (issue4512) Since 13c0327eeb6f, null parent is explicitly excluded. So, there is no reason to have nullrev in the initial seen set.

log: use rev() to build revset of --follow option from numeric revision startrev can be -1.

revset: allow rev(-1) to indicate null revision (BC) This can simplify the conversion from numeric revision to string. Without it, we have to handle -1 specially because repo['-1'] != repo[-1]. The -1 revision is not officially documented, but this change makes sense assuming that "rev(%d)" exists for scripting or third-party tools.

extensions: don't quit loading extensions in the middle if traceback is on This was introduced way back in 2006 (rev 1f6d520557ec) as sys.exit(0) if loading an extension failed when --traceback was on, then at some point morphed into a 'return 1' in a function that otherwise returns nothing. At this point, if ui.traceback is enabled and if loading an extension fails for whatever reason, including one as innocent as it not being present, we leave any extensions loaded so far in a bogus half-initialized state. That doesn't really make any sense.