Solution for "No definition for XXX" gem installation errors

Hello.

I had a problem with RDoc when installing various gems (mysql,
mongrel). I often got error messages of the kind "No definition for
XXX". When doing a google search with that error then it seems that a
lot of people do have that problem. I never read a solution (most
recommend to simply suppress the generation of the documentation). But
a simple "gem install rdoc-data" seems to solve the problem. I don't
know why (maybe you can tell me?!), but it works.

Best regards,
Kai