patches: serial message processing, memory leaks eliminated

Here is a big bundle of patches with respect to ifile 1.0.11 that
serialize message processing.  With these, hopefully you can process a
large folder without running out of memory.

These patches also fix a number of major memory leaks.  Compiled with
the dmalloc debugging malloc library, ifile now looks pretty clean for
-q and -i; I haven't tested all the other options, but I'd be
surprised if there were any problems.

Sad note: proper memory management (i.e. freeing unused memory) may
actually reduce performance in cases where you weren't running out of
memory.  I suspect it's sub-noise, though, compared with the cost of
the actual filtering; I'll be quite interested to hear if people find
things to be otherwise.

Jeremy