to pass a core_options object to the constructor, along with
a search path. This required pushing either a running_machine
or a core_options through some code that wasn't previously
ready to handle it. emu_files can be reused over multiple
open/close sessions, and a lot of core code cleaned up
nicely as things were converted to them.
Also created a file_enumerator class for iterating over files
in a searchpath. This replaces the old mame_openpath functions.
Changed machine->options() to return a reference.
Removed public nvram_open() and fixed jchan/kaneko16 to
stop directly saving NVRAM.
Removed most of the mame_options() calls; this will soon go
away entirely, so don't add any more.
Added core_options to device_validity_check() so they can be
used to validate things.