Mostly some pedantic changes such that `make clean' always ignores
errors. Also changed the top clean target to do the `touch
configs/current' dance instead of realclean.
Seperate the Doxygen configuration files (for full Mesa only) in a common part and an individual module part.
Rewrite the Makefile in order to avoid the double pass when the tag files already exist. A double pass can still be achieved by doing 'make clean all'.