Performance fix for Pathname#chop_basename

This is an internal method, but is called a bunch of times in
performance-critical codepaths, and is ultra slow because the constant
is interpoplated into the Regexp each time the method is called.

Alas, this has been fixed in Ruby 1.9+.

Library/Homebrew/extend/pathname.rb

@@ -386,6 +386,18 @@ class Pathname
     end
   end
 
+  if RUBY_VERSION <= "1.8.7"
+    alias_method :old_chop_basename, :chop_basename
+    def chop_basename(path)
+      base = File.basename(path)
+      if /\A#{Pathname::SEPARATOR_PAT}?\z/o =~ base
+        return nil
+      else
+        return path[0, path.rindex(base)], base
+      end
+    end
+    private :chop_basename
+  end
 end
 
 # sets $n and $d so you can observe creation of stuff