Add sample external commands: dirty, leaves, options

See:

* http://github.com/mxcl/homebrew/issues/issue/1359
* http://github.com/mxcl/homebrew/issues/issue/1438

Library/Contributions/examples/brew-dirty.rb

@@ -0,0 +1,7 @@
+# See: http://github.com/mxcl/homebrew/issues/issue/1359
+
+to_list = HOMEBREW_CELLAR.children.select { |pn| pn.directory? }
+to_list.each do |d|
+  versions = d.children.select { |pn| pn.directory? }.collect { |pn| pn.basename.to_s }
+  puts "#{d.basename} (#{versions.join(', ')})" if versions.size > 1
+end

Library/Contributions/examples/brew-leaves.rb

@@ -0,0 +1,9 @@
+# See: http://github.com/mxcl/homebrew/issues/issue/1438
+
+require 'formula'
+deps_graph = Formula.get_used_by
+formulas = HOMEBREW_CELLAR.children.select { |pn| pn.directory? }.collect { |pn| pn.basename.to_s }
+formulas.each do |name|
+  deps = deps_graph[name] || []
+  puts name if !deps.any? { |dep| formulas.include?(dep) }
+end

Library/Contributions/examples/brew-options.rb

@@ -0,0 +1,9 @@
+ARGV.formulae.each do |f|
+  f.options rescue next
+  puts f.name
+  f.options.each do |o|
+    puts o[0]
+    puts "\t"+o[1]
+  end
+  puts
+end