At least docbook2man inserts a date formatted using the current
locale into its output.

Reviewed-by: iustinp

This change allows us to use cleaner dependencies between
directories. The build system is basically rewritten in large parts
and may contain bugs.

Reviewed-by: iustinp

This patch adds checking for our external python modules at the
./configure stage, as it's better to check than rely on documentation.

The patch adds one autoconf macro from the autoconf macro archive
(http://autoconf-archive.cryp.to)

Reviewed-by: imsnah