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* the current patch levels hard-coded here are pretty dated. I updated the ruby version helpers to use loose ruby version matchers so they don't continually need to be updated with every new patch level release.

* `rvm get head` actually performs an `rvm reload` in the post install. there's no need to do again here in rvm-update so I've removed that.

Signed-off-by: Joni Chandra <joniliciously@gmail.com>

Ruby version numbers update:
1.8.7-p371
1.9.3-p392
2.0.0-p0

1) be gentle - first git pull request
2) added ruby 2.0.0 alias and function

sorin-ionescu had some good points.

Add helper function to list gems in a pretty way (only with rvm, for now). Add
missng EOF newline and a todo to the ruby plugin.

Add helper function to get rvm head. Add helper function to link zsh
completion that comes with rvm into om-my-zsh plugin directory, but don't
overwrite the completion that comes with oh-my-zsh (oh-my-zsh's completion is
better, but I want to be able to compare).

Add alias to list installed rubies. Add alias to list gemsets in active ruby.

Add helper functions to switch gemsets on ruby-1.8.7-p334 and ruby-1.9.2-p180.
Add completion definitions for helper functions.