The patch allows to use autoreconf, replaces some long obsolete
constructs and does some other minor cleanups. Also, the file
configure.in is renamed to configure.ac, as the old name has been
deprecated for a long time.
Thanks to Ruben Kerkhof for the patchset.
C includes as they contain substitutions specific to make.
Worked around by creating sysconf/paths.h which is created from
the Makefile instead of by the configure script.
All documentation is built in obj/doc (resp. doc/ if you do a stand-alone build).
Use `make docs' to make the whole documentation or `make userdocs' resp.
`make progdocs' for user manual resp. developer's guide.
