Change to_d to to_deg

Ruby 1.9 introduced  to_d, for to double, which conflicted with my use
of to_d as and alias for to degrees.  Hence to_d has been changed to
to_deg.

Also added to_rad as an alternate alias to to_r. The aim is to
eventually remove the to_r.
Rakefile comented out rubyforge_name

variable rubyforge_name is no longer valid in Hoe, so comented it out.
Gem v1.6 makes fine, and tests were successful.