Don't bottle unless built with correct flag.

Closes Homebrew/homebrew#9350.

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

Library/Contributions/examples/brew-bottle.rb

 # Builds binary brew package
-require 'cmd/install'
+require 'tab'
 
 ARGV.each do|formula|
   # Get the latest version
@@ -12,9 +12,16 @@ ARGV.each do|formula|
 
   source = HOMEBREW_CELLAR + formula + version
   filename = "#{formula}-#{version}-bottle.tar.gz"
-  ohai "Bottling #{formula} #{version}..."
   destination = Pathname.pwd
+
+  tab = Tab.for_keg source
+  if not tab.built_bottle
+    onoe "Formula not installed with '--build-bottle': #{formula}"
+    next
+  end
+
   HOMEBREW_CELLAR.cd do
+    ohai "Bottling #{formula} #{version}..."
     # Use gzip, faster to compress than bzip2, faster to uncompress than bzip2
     # or an uncompressed tarball (and more bandwidth friendly).
     safe_system 'tar', 'czf', destination/filename, "#{formula}/#{version}"