Globally rename the header inclusion guard names.

Consistently apply this rule: the guard name is obtained from the
filename by stripping the leading "lib", converting '/' and '.'  to
'_' and uppercasing the resulting name. Guard names in the root
directory have to be prefixed by "FFMPEG_".

Originally committed as revision 15120 to svn://svn.ffmpeg.org/ffmpeg/trunk
diff --git a/libavcodec/bmp.h b/libavcodec/bmp.h
index cbbd21c..b24a1fa 100644
--- a/libavcodec/bmp.h
+++ b/libavcodec/bmp.h
@@ -19,8 +19,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#ifndef FFMPEG_BMP_H
-#define FFMPEG_BMP_H
+#ifndef AVCODEC_BMP_H
+#define AVCODEC_BMP_H
 
 #include "avcodec.h"
 
@@ -35,4 +35,4 @@
     BMP_BITFIELDS   =3,
 } BiCompression;
 
-#endif /* FFMPEG_BMP_H */
+#endif /* AVCODEC_BMP_H */