more robust test for presence of unpacked rspec gem from rspec.rake
more robust test for presence of unpacked rspec gem from rspec.rake

- allows for github gems (prefixed with github account, like dchelimsky-rspec-1.1.11.2)
- checks for presence of spec/rake/spectask.rb, which is what the generated rspec.rake file needs to load anyhow

dchelimsky/rspec-rails,patmaddox/rspec2rails2,weplay/rspec-rails,mcmire/rspec-rails