phantomjs: Yosemite fixes.

Closes Homebrew/homebrew#32953.

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

Library/Homebrew/requirements.rb

@@ -6,6 +6,7 @@ require 'requirements/mpi_dependency'
 require 'requirements/osxfuse_dependency'
 require 'requirements/python_dependency'
 require 'requirements/x11_dependency'
+require 'requirements/maximum_macos_requirement'
 
 class XcodeDependency < Requirement
   fatal true

Library/Homebrew/requirements/maximum_macos_requirement.rb

@@ -0,0 +1,19 @@
+require 'requirement'
+
+class MaximumMacOSRequirement < Requirement
+  fatal true
+
+  def initialize(tags)
+    @version = MacOS::Version.from_symbol(tags.first)
+    super
+  end
+
+  satisfy { MacOS.version <= @version }
+
+  def message
+    <<-EOS.undent
+      OS X #{@version.pretty_name} or older is required for stable.
+      Use `brew install devel or --HEAD` for newer.
+    EOS
+  end
+end