avoiding build dependency on docbook, etc. in new port

[Charlie Kester]

I'm porting some software that has a build dependency on docbook2man in
order to generate its manpages from .docbook files.

Testing the port in tinderbox takes a long time, most of it because of
the need to build the docbook infrastructure.  It seems a shame to use
all that CPU time and install all those packages just to get ready to
convert some manpages. 

What's the preferred approach in cases like this?  Should I keep the
build dependency on docbook2man et al, or should I put pregenerated
copies of the manpages in the files directory of the port?