ruby has default gems search paths; let it handle defaults

this will probably fail on rubies older than 1.9ish but i need
more representative data to come up with a viable solution to
forcibly setting gem search paths. it should probably prefer some
value of $HOME or ~ plus .gems/ (?). this is suboptimal for
Windows users, however, but http://docs.rubygems.org/read/chapter/12#page53 says that rubygems already tries various methods for
deriving the user's home directory. preferably we could leverage
this in chrubylib, and let rubygems do the heavy lifting.

that turns this into a matter of reliably making "require 'rubygems'
work under any circumstance excepting that 'rubygems' actually is
not available at all. research and verification required.