Remove require 'rubygems' as it's always available

Rake requires Ruby 1.9 or newer which always has a RubyGems available.
Remove rcov tasks

rcov does not work on Ruby 1.9 or newer and I don't at present care
about using simplecov.
Remove unused plugin method

It seems to be for files I don't have or were in Jim's RUBY_LIB.
Remove where_am_i task

I do not know what it is for
Remove failure, really_fail tasks

I do not know what they are for
Remove loading of publish and xforge rakefiles

I think these only exist on Jim's computer.  I will not need them once
rake is using hoe for releases.
Remove unused noop task
Remove svn-specific release tasks

rake has been on git for many years now.
Remove direct install capability

I don't see a need for keeping this around.  You should install via a
gem nowadays.
Remove rdoc existence checks

Ruby 1.9+ (at least 1.9.3+) has a version of rdoc for which the checks
are all true.
There are no CVS tasks anymore
Switch to hoe

This converts the major tasks (release and documentation generation,
mainly) to using hoe.
Remove support tasks

I do not need to count lines in rake or see where TODOs are
Remove flog/flay tasks

Hoe provides these already
Remove tags task

The rdoc-tags gem provides this task via hoe
Update manifest for rakelib removals