Shuffle order of __muncher()'s args.

Since bok and pid are only ever used together, pass them together in
the argument list, rather than with (unrelated) fatal in between.
Restore separating of leaks from other issues.

Include file descriptor leaks as leaks; add a common base for Leak and
FDLeak, based on Issue; test against this to distinguish leaks; and
separate out based on this when copying a thread's issues out into the
primary collections.
Move Thread class.

It's not a mere place-holder any more.  Also document it a bit.
Fix handling of first line after cruft.

If a waffle block ends by recognising the first line after it, I was
assuming that line must be non-waffle - of course, it might be the
start of a fresh waffle block, so check for that, too.
fixup! Made leak's size details into a vector.

LeakSize.fromParsed() would return a tuple if unsure, where it should
have returned a LeakSize() instance made from that tuple !
fixup! Finish up rework and add support for file descriptors.
fixup! Cope with a few more quirks.