Allows metadata to override the type of Rails spec

[Fixes #801]
Default value for metadata.
Memoizes the regular expressions for path matching
Revert "Default value for metadata."

This reverts commit 427983ae09e1a1eac650ba0a1eaeb876c23054aa.

This syntax is not supported on Ruby 1.8.7

Conflicts:
	lib/rspec/rails/example.rb
Merge pull request #807 from rspec/issue-801-overridding-spec-types

Allows metadata to override the type of Rails spec