Print an appropriate message if the tapped repository appears to be private

Closes Homebrew/homebrew#12247.
Closes Homebrew/homebrew#12244.

Signed-off-by: Max Howell <mxcl@me.com>

Library/Homebrew/cmd/tap.rb

@@ -29,6 +29,22 @@ module Homebrew extend self
     tapd.find_formula{ |file| files << tapd.basename.join(file) }
     tapped = link_tap_formula(files)
     puts "Tapped #{tapped} formula"
+
+    # Figure out if this repo is private
+    # curl will throw an exception if the repo is private (Github returns a 404)
+    begin
+      curl('-Ifso', '/dev/null', "https://api.github.com/repos/#{repouser}/homebrew-#{repo}")
+    rescue
+      puts
+      puts "It looks like you tapped a private repository"
+      puts "In order to not input your credentials every time"
+      puts "you can use git HTTP credential caching or issue the"
+      puts "following command:"
+      puts
+      puts "   cd #{tapd}"
+      puts "   git remote set-url origin git@github.com:#{repouser}/homebrew-#{repo}.git"
+      puts
+    end
   end
 
   def link_tap_formula formulae