This is deemed quite useless now and we should not be littering the file
system with .mediaartlocal directories everywhere.

https://bugzilla.gnome.org/show_bug.cgi?id=722795

Part of this API changes makes the media_art_get_{path|file}() APIs not do
i/o operations like creating the cache directory. This is now done in
media_art_process_new().

https://bugzilla.gnome.org/show_bug.cgi?id=724879

https://bugzilla.gnome.org/show_bug.cgi?id=724879

Part of this API changes makes the media_art_get_{path|file}() APIs not do
i/o operations like creating the cache directory. This is now done in
media_art_process_new().

https://bugzilla.gnome.org/show_bug.cgi?id=724879

The function media_art_get_file checks for null values in artist, title and
prefix arguments, and puts special values on them if they do.

Do the same on media_art_get_path which calls media_art_get_file internally.

https://bugzilla.gnome.org/show_bug.cgi?id=727478

https://bugzilla.gnome.org/show_bug.cgi?id=731681

AutoMake warning += vs = for EXTRA_DIST/CLEANFILES

Also added some checks into the API and a return value to know if the function
was successful.

https://bugzilla.gnome.org/show_bug.cgi?id=734837

Also updated the unit tests so they don't fail with the new tap system

This is quite an API break, but the previous API was confusing and a monster,
so this was really necessary.

The unit tests have been put in place to make sure things work correctly too.

Use $top_srcdir, not relative links

Use CC_CHECK_FLAGS_APPEND m4 macro to make sure GCC supports flags

This is after finding out that some platforms or versions of GCC don't
support flags like -Wmaybe-uninitialized

The attributes.m4 is stolen from systemd who stole it from xine-lib.