This gets rid of OpenWithError(), and just always returns a negative value
on error for OpenFile(). Also fixed the sequence rollover, which could've
returned 0.
0 should be considered a valid handle ideally, but left it never returning
0 to simplify cleanup in some areas.
This tries to execute them within the context of the emulator as much as
possible, so we don't have weird bugs. Going with a file type so we can
easily load the dump by opening the file directly.
