Check gem dependencies before installation

With gem dependency it is possible to check the dependencies for your gem before you install it.

Here is an example output for Nokogiri:

Gem nokogiri-1.4.4
  hoe (>= 2.6.2, development)
  minitest (>= 1.6.0, development)
  racc (>= 0, development)
  rake-compiler (>= 0, development)
  rexical (>= 0, development)
  rubyforge (>= 2.0.4, development)