SQLite 3.7.3 is the version shipped in Debian Squeeze (oldstable);
should be old enough to be the required version.  Drop the
compatibility #ifdef.

Don't assume "-lpthread".  Just use PTHREAD_CFLAGS, as determined by
AX_PTHREAD.

Works around a linker problem with some older glibc versions: if
"-lrt" was used, then "-pthread" was implied, but only the symbols
used by librt were available.  This led to a linker error because
pthread_atfork() was not found.

So with "-lrt", autoconf decides that no pthread flag is necessary,
but in the end fails due to pthread_atfork() missing.

By checking for pthread before librt, we avoid this dependency
problem.

Replaces the old options --with-tremor-libraries and
--with-tremor-includes.

Don't imply the library's name is "vorbisidec"; use whatever we found
inside TREMOR_LIBS.

Require the version 2 which has a more sane API.

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.

Remove our own songlength database parser.

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.

libmp4v2 is licensed under MPL 1.1, which is incompatible with GPLv2.
Unfortunately, this means that we must remove the plugin.

More information can be found in the Debian bug report:

 http://bugs.debian.org/767504

Simplify the definition of many build options.