Raise on JRuby 1.7.3 warning Celluloid is broken

After helping someone debug this *again* today I think our best bet is
to simply have Celluloid raise if someone tries to require it on JRuby
1.7.3:

    $ bundle exec irb -rcelluloid
    RuntimeError: Celluloid is broken on JRuby 1.7.3. Please upgrade to
    1.7.4+
Merge pull request #307 from celluloid/blow-up-on-jruby-173

Raise on JRuby 1.7.3 warning Celluloid is broken
Specify full path for sysctl on darwin hosts
Merge pull request #308 from amrik/master

Specify full path for sysctl on darwin hosts
Add a backtrace to the Task termination exception
Set the task status to running before raising the resumable error
Package entire specs with gem

Fixes #263
Merge pull request #311 from celluloid/task-terminate-backtrace

Add a backtrace to the Task termination exception
guard-rspec doesn't take a version number any more
Auto-run relevant specs when shared examples are modified
Highlight Ruby syntax in README.
Merge pull request #315 from parndt/patch-1

Highlight Ruby syntax in README.
Moved Celluloid#version to lib/celluloid.rb

This fixes #316
Merge pull request #316 from parndt/version_class

Use a Celluloid::Version class instead of a constant.
Note 0.15 CHANGES
Merge pull request #7 from celluloid/master

Catch up!!!