Add a configure option '--disable-doc' to disable building of the
documentation by the 'all' target.
Check for the required tools at configure time, and require them if
building documentation is enabled.
Even if building the documentation was diabled with '--disable-doc',
'make -C doc' at the top
Add patch, and make cocom unconditional in list of build prerequisites.
Even though the products of these tools are checked in, these are tools
are required when building in a fresh git checkout, presumably due to
the order in which git creates the files resulting in timestamps which
indicate that
