Making JSON-RPC accept more content types

According to the RFC for JSON-RPC over HTTP at
http://www.jsonrpc.org/historical/json-rpc-over-http.html
"Content-Type SHOULD be 'application/json-rpc' but MAY be
'application/json' or 'application/jsonrequest'"

This patch fixes HTTPJsonRpcHandler to allow for any of those three
content types when accepting JSON-RPC HTTP requests.

This also fixes compatibility with the popular Python library jsonrpclib
which uses the application/json-rpc content type.
[codegenerator] Helper.groovy: fix typo
[codegenerator] Helper.groovy: add support for class variables
[codegenerator] python: extend IN typemap to support int, double and float
renderer: replace render buffer indices with queues
renderer: simplify code by always maintaining one front buffer
renderer: remove now pointless GetNext(Decode/Render) function
renderer: name present buffer structure to be able to reference it
renderer: store bypass format in rendermanager instead

The present method will be overwritten on each flippage
renderer: drop copies of variables, use queue data directly
renderer: grab presentlock in AddVideoPicture
DVDAudioCodecFFmpeg: Grow the resampling buffer as needed instead of allocating it an arbitrary big size.
DVDAudioCodecFFmpeg: Remove write only assignment.
DllAvFilter: Always include libavfilter/buffersrc.h for av_buffersrc_add_frame.
[codegenerator] python: extend swig template to support class variables
[legacy] hide C++ only public class variables from swig
python: don't consider scripts which threw an exception as successful
[Linux] Read OS information from /etc/os-release
Most modern Linux distributions use the /etc/os-release
file for operating system information.
This patch will try to read the PRETTY_NAME variable from
/etc/os-release to identify the Linux distribution.

If /etc/os-release doesn't exist, the code will still fall back
to lsb_release or the distro-specific release files.

http://www.freedesktop.org/software/systemd/man/os-release.html
http://0pointer.de/blog/projects/os-release.html
update wunderground addon
removed: BackGroundInfo Loader multithreading (no longer needed)