Add some common error types.
Add some common error types.

I don't want to go overboard with this, but some things are so extremely frequent in the wild that having them jotted down in a handy place seems warranted.

Signed-off-by: Eric Myhre <2346ad27d7568ba9896f1b7da6b5991251debdf2@exultant.us>

polydawn/meep,polydawn/meep