New x11grab patch for ffmpeg

Courtesy of Edouard Gomez, we have a new x11grab patch for ffmpeg. According to his mail, the following things are new:

• use av_log, no fprintf
• remove unnecessary strdup of ap->device
• some cleaning and code homogeneity
• rebase on current (~20060902) ffmpeg SVN

Grab it here. This patch includes bug fixes contributed by Ali Servet Donmez. Thanks both of you!