Fix broken URL in entdec.c.

Thanks to thinqa for the report.
Fixes #1968.
Update the RTP draft for resubmit
Fixes a denorm issue in the VoIP mode high-pass filter
Fix relative paths the header file in the VS2010 projects.

This prevented opening the files from the 'Solution Explorer'
interface where the source listing is displayed. Thanks to
Koen Vos for reporting the issue.
Fix more VS2010 header paths.