output/httpd: rename struct httpd_output
output/httpd: move functions into the HttpdOutput class
audio_config: include cleanup
db/Proxy: explicitly request first element of array

Works around gcc 4.6 bug.
decoder/mp4ff: delete obsolete plugin

The underlying library has been obsolete for many years.
decoder/ffmpeg: require ffmpeg/libav 0.7.6

This is the version present in Ubuntu Oneiric, the oldest distribution
with gcc 4.6.  Debian Squeeze is off target, because it has gcc 4.4,
which is unable to compile MPD anyway.

This commit drops all API compatibility hacks for older versions.
input/ffmpeg: rename the class
input/ffmpeg: add constructor/destructor
input/soup: rename the class
input/Soup: move code into the class
DatabaseLock, input/bzip2: remove obsolete Glib/gcc workaround
archive/bzip2: rename the classes
input/bzip2: add constructor/destructor
input/zzip: rename the classes
input/zzip: add constructor/destructor
input/iso9660: rename the classes
input/iso9660: add constructor/destructor
input/despotify: rename class
input/despotify: add constructor/destructor
InputStream: add constructor/destructor

Eliminate input_stream_init() and input_stream_deinit().