subrepo: rewrite handling of subrepo state at commit (issue2403) When the contents of .hgsubstate are stale (either because they've manually been tweaked or partial updates have confused it), we get confused about whether it actually needs committing. So instead, we actively consult the parent's substate and compare it the actual current state when deciding whether it needs committing. Side effect: lots of "committing subrepo" messages that didn't correspond with real commits disappear. This change is fairly invasive for a fairly obscure condition, so it's kept on the default branch.

subrepo: add basestate method This will allow us to sort out what's going on with state .hgsubstate files more precisely.

bdiff: fix malloc(0) issue in fixws() If fixws() is called on a zero-length string, malloc(0) is called and expected to return a pointer. Which it does on e.g. Linux. AIX returns NULL, which it is also legal, but the malloc() is then assumed to have failed. So ensure a valid pointer is always returned.