More changes to the new docker based build system.
* autogen.sh: Update from gpgrt to fix leading double slash. * build.sh: Major changes to adjust for the new build system. * configure.ac: Change the default build directory to "~/b/SRCDIRNAME-playground". * src/Makefile.am: Simplify setting of the top directories. (stamp-rtlib-files): Fix c+p bug. Create the stamp dir. * src/nsis/inst-gpg4win.nsi: Take the slides from the soruce dir.
Note that not all options have been tested.