* Use the plugin data folder for storing the cache. The history folder
may be read-only or shared with different configurations.
* Don't create the cache database or surrounding folder if there's
nothing to store in it.
* Actually use prepared queries multiple times rather than always
destroying them after a single use.
* Added proper error checking for most database operations.
* Improved query performance by avoiding outer joins and table scans.
-bus/nubus: Made the Macintosh Display Cards map the blue channel to
white with monochrome monitors. Also added logging for PLL
configuration to help debug how CRTC and RAMDAC clocks work in the
future.
* bus/nubus: Started emulating SuperMac Spectrum/8 CRTC.
* bus/nubus: Respect Apple 4•8 screen base register.
* cpu/m68000: Fixed disassembly of bit field extract instructions.
* Also cleaned up data plugin a little.
