Moved the intricacies of the perl interface build into its own makefile

that now functions as a wrapper around the MakeMaker stuff. It might
even behave sensically when we have separate build dirs. Same for plperl,
which of course still doesn't work very well. Made sure that plperl
respects the choice of --libdir.

Added --with-python to automatically build and install the Python interface.
Works similarly to the Perl5 stuff.

Moved the burden of the distclean targets lower down into the source tree.
Eventually, each make file should have its own.

Added automatic remaking of makefiles and configure. Currently only for the
top-level because of a bug(?) in Autoconf. Use GNU `missing' to work around
missing autoconf and aclocal. Start factoring out macros into their own
config/*.m4 files to increase readability and organization.