Log Message:
Update ruby200-base to 2.0.0p643.

This is the last ordinal release of Ruby 2.0.0. Ruby 2.0.0 goes into the
state of the security maintenance phase, and will never be released unless
any critical regressions or security issues are found. This phase is planned
to be maintained for 1 year. Then, maintenance of Ruby 2.0.0 will be ended
at Feb. 24th, 2016. We recommend to start planning to migrate to newer
versions of Ruby, such as 2.1 or 2.2.

pkgsrc change:

* Change "os" of Gem::Platform, now it change the case of \ 
"netbsd" only.
* Reduce patches to builtin rubygems.