Mupen64 64-bit: Some changes + plugins ported over

A few changes, plus got tired of checking out to the original state of the repository every time I needed to re-obtain stable 64-bit compiles of the plugins originally shipped with Mupen64 0.5.

Mupen64 for x86-64 plugin developers

Experiment designed to be able to develop and test RCP emulation plugins for portability to 64-bit UNIX-based systems.

In the process of fixing the core to allow 64-bit CPU emulation and plugins, a few incidental fixes were made on the side. Generally the only focus has been getting the interpreter to work in 64-bit, but from the top a few bugs in the GTK UI and things like a crash in unimplemented flash read (tested with Pokémon Snap) were fixed, along with several compiler warnings concerning C malpractice.

Other than that, most ROMs that do not work on the original Mupen64 0.5 release by Hacktarux continue to not work in this one either, due to focusing on preservation of his original methods along with a lack of investigation. Some tracing was added to diagnose when the RSP falls into a permanent CPU loop for some titles; this again has not been fully investigated.

Plugins will have to be found elsewhere since the native 32-bit plugin sources were omitted from this fork.