What seems to have happened is that gem_runner is no longer required
automatically when you require rubygems. It appears to be an
intentional change in rubygems, as a part of "slimming" it down for
inclusion in 1.9
The trivial fix is to add a line to require the rubygems/gem_runner.rb
A quick check of the rubygems commit logs reveals that there could be
a fix down the line (r1515 will apparently "faults in the full
rubygems library if any Gem constant or method is called.") so it
might not be worthwhile actually patching this.
--- railties/lib/tasks/framework.rake (revision 8220)
+++ railties/lib/tasks/framework.rake (working copy)
@@ -4,6 +4,7 @@
task :gems do
deps = %w(actionpack activerecord actionmailer activesupport
+ require 'rubygems/gem_runner'
rails = (version = ENV['VERSION']) ?