Add TapDependency

Library/Homebrew/dependency.rb

@@ -131,3 +131,15 @@ class Dependency
     end
   end
 end
+
+class TapDependency < Dependency
+  def initialize(name, tags=[], env_proc=DEFAULT_ENV_PROC, option_name=name)
+    super(name, tags, env_proc, name.split("/").last)
+  end
+
+  def installed?
+    super
+  rescue FormulaUnavailableError
+    false
+  end
+end

Library/Homebrew/dependency_collector.rb

@@ -89,6 +89,8 @@ class DependencyCollector
       Dependency.new(spec, tags)
     elsif (tag = tags.first) && LANGUAGE_MODULES.include?(tag)
       LanguageModuleDependency.new(tag, spec)
+    elsif HOMEBREW_TAP_FORMULA_REGEX === spec
+      TapDependency.new(spec, tags)
     else
       Dependency.new(spec, tags)
     end

Library/Homebrew/test/testing_env.rb

@@ -27,6 +27,8 @@ HOMEBREW_WWW           = 'http://example.com'
 HOMEBREW_CURL_ARGS     = '-fsLA'
 HOMEBREW_VERSION       = '0.9-test'
 
+HOMEBREW_TAP_FORMULA_REGEX = %r{^(\w+)/(\w+)/([^/]+)$}
+
 RUBY_BIN = Pathname.new(RbConfig::CONFIG['bindir'])
 RUBY_PATH = RUBY_BIN + RbConfig::CONFIG['ruby_install_name'] + RbConfig::CONFIG['EXEEXT']