* Makefile.am: Add option for building gpgsum
* autogen.rc: Add option for building gpgsum
* configure.ac: Add option for building gpgsum
* tools/Makefile.am: Add sources for gpgsum
* tools/gpgsum-w32info.rc: Add new file
* tools/gpgsum.c: Add gpsum tool
* tools/gpgsum.w32-manifest.in: Add new file
