Fix sce_lbn handling

Fixes a few games that weren't starting, fixes #212 (at least, the game loads for me), maybe / maye not fixes #343 (don't have that one to check.)

The changes:
 * allow sce_lbn%x_size%x (with lots of logging in case there's more variants), not just sce_lbn0x%08x_size%x08x.
 * allow seeking on a sce_lbn virtual file.
 * actually respect the mount option in headless.
 * fail for sce_lbnfffffff etc. that would be outside the iso.

And I also threw in making prefix matching case insensitive (because disC0:/ works fine too.)  I don't know that it will actually affect any games.

All of these were verified on a real PSP but, it's kind of hard to write a good test for this...

-[Unknown]