exceptions: improve tap error message.

Point users to the tap's issue tracker URL.

Library/Homebrew/exceptions.rb

@@ -183,7 +183,10 @@ class BuildError < Homebrew::InstallationError
       puts
       puts "#{Tty.red}READ THIS#{Tty.reset}: #{Tty.em}#{ISSUES_URL}#{Tty.reset}"
       if formula.tap?
-        puts "If reporting this please do so at the #{formula.tap} tap (not mxcl/homebrew)."
+        user, repo = formula.tap.split '/'
+        tap_issues_url = "https://github.com/#{user}/homebrew-#{repo}/issues"
+        puts "If reporting this issue please do so at (not mxcl/homebrew):"
+        puts "  #{tap_issues_url}"
       end
     else
       require 'cmd/--config'