add myself as build system maintainer

Originally committed as revision 5495 to svn://svn.ffmpeg.org/ffmpeg/trunk

MAINTAINERS

@@ -45,7 +45,7 @@ Miscellaneous Areas
 
 documentation                           Mike Melanson, Diego Biurrun
 website                                 Mike Melanson, Diego Biurrun
-build system (configure,Makefiles)      Diego Biurrun
+build system (configure,Makefiles)      Diego Biurrun, Mans Rullgard
 project server                          Diego Biurrun, Mans Rullgard