title: Rails keeps telling me that it's not currently installed
body: <p>I use <code>rvm</code> to manage different rubies and their gemsets. My shell is zsh with oh-my-zsh configured with basic settings. Enabled oh-my-zsh plugins are ruby, rails, osx, and git. Here's the command I used to install ruby-1.8.7 and rails-3.0.7.</p>
  
  <pre><code>rvm install 1.8.7
  rvm use 1.8.7
  gem install rails -v=3.0.7
  </code></pre>
  
  <p>and then I typed <code>rails</code> and got:</p>
  
  <pre><code>Rails is not currently installed on this system. To get the latest version, simply type:
  
      $ sudo gem install rails
  
  You can then rerun your "rails" command.
  </code></pre>
  
  <p>I've tried more thorough installs also, Like reinstall <code>rubygems</code> after switching to ruby-1.8.7, or create a completely new gemset, but with no luck.</p>
  
  <p>Here's the rvm info:</p>
  
  <pre><code>ruby-1.8.7-p352@rails:
  
    system:
      uname:       "Darwin yicai.local 10.8.0 Darwin Kernel Version 10.8.0: Tue Jun  7 16:32:41 PDT 2011; root:xnu-1504.15.3~1/RELEASE_X86_64 x86_64"
      bash:        "/bin/bash =&gt; GNU bash, version 3.2.48(1)-release (x86_64-apple-darwin10.0)"
      zsh:         "/bin/zsh =&gt; zsh 4.3.9 (i386-apple-darwin10.0)"
  
    rvm:
      version:      "rvm 1.8.6 by Wayne E. Seguin (wayneeseguin@gmail.com) [https://rvm.beginrescueend.com/]"
  
    ruby:
      interpreter:  "ruby"
      version:      "1.8.7"
      date:         "2011-06-30"
      platform:     "i686-darwin10.8.0"
      patchlevel:   "2011-06-30 patchlevel 352"
      full_version: "ruby 1.8.7 (2011-06-30 patchlevel 352) [i686-darwin10.8.0]"
  
    homes:
      gem:          "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails"
      ruby:         "/Users/nil/.rvm/rubies/ruby-1.8.7-p352"
  
    binaries:
      ruby:         "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin/ruby"
      irb:          "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin/irb"
      gem:          "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin/gem"
      rake:         "/Users/nil/.rvm/bin/rake"
  
    environment:
      PATH:         "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails/bin:/Users/nil/.rvm/gems/ruby-1.8.7-p352@global/bin:/Users/nil/.rvm/rubies/ruby-1.8.7-p352/bin:/Users/nil/.rvm/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/local/sbin"
      GEM_HOME:     "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails"
      GEM_PATH:     "/Users/nil/.rvm/gems/ruby-1.8.7-p352@rails:/Users/nil/.rvm/gems/ruby-1.8.7-p352@global"
      MY_RUBY_HOME: "/Users/nil/.rvm/rubies/ruby-1.8.7-p352"
      IRBRC:        "/Users/nil/.rvm/rubies/ruby-1.8.7-p352/.irbrc"
      RUBYOPT:      ""
      gemset:       "rails"
  </code></pre>
  
  <p>and the gem version is 1.8.10, the latest.</p>