Since version 2.32, g_thread_init() is deprecated and a no-op.  Let's
upgrade that (optional) dependency so we can remove all those
g_thread_init() calls.

Only very few (minor) features still depend on GLib.

These do not require GLib anymore.

Don't use GLib.

Eliminate duplicate SidTune construction.

Remove our own songlength database parser.

Eliminates duplicate ParseContainerPath() call.

Replaces g_ascii_strup() and allows building the Vorbis encoder
without GLib.

Replaces GLib's g_strsplit().

Use simple string and path parsing functions instead of GLib's
g_pattern_match(), which was used in a very clumsy way.

There is duplicate code in the two.