Remove completion for nonexistent ':show information'
Fix spelling of various strings.

I dumped `strings barnowl.bin` into a file and ran it through ispell,
and then excluded libfaim corrections.
Fix a memory leak in zcrypt.c, caught by clang scan-build
Die on a failed zephyr_zwrite; don't silently ignore it
Fix some undefined behavior in filter.c, caught by clang scan-build
Make :loadsubs reload instanced personals too

Right now if your subs get lost because something falls over, you have
to manually sub to instanced personals to get them back. :loadsubs
doesn't work.

(Supposedly that code is for "backwards compatibility", but... it dates
back to kretch. Probably because it's odd that :loadsubs [file] will
also automatically load the default subs. But given that everyone runs
:loadsubs with no argument to mean "oops zephyr fell over reload my subs
please", I'm okay with adding more code to the "backwards compatibility"
path. I doubt anyone actually runs :loadsubs with an argument anyway.)

Also, while I'm here, get rid of that 'foo' variable. (Really? Really?!
foo?!?)