rdmd for GDC

[Anders F Björklund]

Not sure if this had already been done elsewhere,
but here's a port of "rdmd" over to GDC and Unix:

http://www.algonet.se/~afb/d/rdmd.d
(tested OK on Mac OS X using GDC 0.23)

Here's a matching manual page, mostly taken from
the help text, that should go with the binary:

http://www.algonet.se/~afb/d/rdmd.1
(goes in man/man1/ next to the bin/)

Basically just ported linux -> Unix, made it default
to gdmd for version(GNU) and fixed some linker issues.

Still in the Public Domain, so enjoy...
--anders


PS. We probably still need a multi-module version,
but that could probably be done using bud/rebuild.