Gem install fails when a source has a version of the gem in which version number contains a string

If a gem has a version number which is appended by a string (for example oauth 0.3.7.pre1), gem install will fail, even if another (stringless) target version of the gem is specified in config.

While this is the only example of the problem I've been able to find, I suspect it may occur whenever a string is contained in a version number at any point, i.e. 1.3.beta.1, etc..

Following is the output:

irb(main):003:0> GemInstaller.install('--config required_gems.yml')
Malformed version number string 0.3.7.pre1
=> 1

And the contents of required_gems.yml:

defaults:
install_options: --include-dependencies --no-rdoc --no-ri gems:
- name: oauth version: '= 0.3.6'

The gem source used is: http://gems.rubyforge.org/

(You can see the offending gem version listed on the oauth gem page here: http://rubygems.org/gems/oauth)