RaspiStill example code for YUV fast paths

Update RaspiStill framework to provide access to the new EGL image
targets that provide a fastpath for mapping the individual YUV planes to
one byte per pixel GL_LUMINANCE buffers. These are still accessed as OES
textures so this is effectively a greyscale image created from a single
plane of a MMAL buffer.

Also added some example code (yuv, sobel) that demonstrates how to use
the new EGL image targets.

Also, add -gc to the command line to capture the GL frame-buffer as a TGA file.

Thanks to Tim Gover

host_applications/linux/apps/raspicam/gl_scenes/mirror.h

@@ -0,0 +1,37 @@
+/*
+Copyright (c) 2013, Broadcom Europe Ltd
+Copyright (c) 2013, Tim Gover
+All rights reserved.
+
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in the
+      documentation and/or other materials provided with the distribution.
+    * Neither the name of the copyright holder nor the
+      names of its contributors may be used to endorse or promote products
+      derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#ifndef MIRROR_H
+#define MIRROR_H
+
+#include "RaspiTex.h"
+
+int mirror_open(RASPITEX_STATE *state);
+
+#endif /* MIRROR_H */