brew-bundle: add new command to support Brewfiles.

Closes Homebrew/homebrew#24107.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Contributions/cmd/brew-bundle.rb

+# Looks for a Brewfile and runs each line as a brew command. For example:
+#
+# tap foo/bar
+# install spark
+#
+# Saving the above commands in a Brewfile and running `brew bundle` will run
+# the commands `brew tap foo/bar` and `brew install spark` automagically.
+#
+# Current discussion: https://github.com/mxcl/homebrew/pull/24107
+
+raise "Cannot find Brewfile" if not File.exist?('Brewfile')
+File.readlines('Brewfile').each do |line|
+	command = line.chomp
+	if not command.empty? and not command.chars.first == '#'
+		`brew #{command}`
+	end
+end