rbug: fix make process on Linux Mint 13 x64.

rbug: fix make process on Linux Mint 13 x64.

Previously, rbug_*.c would fail to compile with incomplete prototype
errors when make was run from the command line on my machine. My IDE
always built fine, and still does after this patch (Netbeans 7.1.2).

Most of the includes from files in gallium/auxiliary/rbug/* were
assuming an rbug/ subdirectory, while the headers are actually in the
same directory as the .c files.

The build error was also previously a problem for me on Ubuntu 11.10
and Mint 12.

Fixes build for the following configuration: ./autogen.sh
--enable-debug --enable-texture-float --with-gallium-drivers=r600
--with-dri-drivers=radeon --enable-r600-llvm-compiler

Signed-off-by: Brian Paul <brianp@vmware.com>