Allow custom matchers to use #match built in

Addresses problem with dispatching the #match matcher from within a
custom matcher. (Wow... what a mouthful) See Issue #188.

features/custom_matchers/define_matcher.feature

@@ -338,3 +338,27 @@ Feature: define matcher
       | 4 examples, 2 failures               |
       | expected 9 to be a multiple of 2     |
       | expected 9 not to be a multiple of 3 |
+
+  Scenario: that match against a regular expression
+    Given a file named "regular_expression_matcher_spec.rb" with:
+      """ruby
+      RSpec::Matchers.define :be_valid_us_zipcode do
+        match do |actual|
+          expect(actual).to match_regex(/\A\d{5}(-\d{4})?\z/)
+        end
+      end
+
+      describe "30316" do
+        it { should be_valid_us_zipcode }
+      end
+
+      describe "30316-0001" do
+        it { should be_valid_us_zipcode }
+      end
+
+      describe "1000-61303" do
+        it { should_not be_valid_us_zipcode }
+      end
+      """
+    When I run `rspec regular_expression_matcher_spec.rb`
+    Then the stdout should contain "3 examples, 0 failures"

lib/rspec/matchers.rb

@@ -491,10 +491,14 @@ def include(*expected)
     #
     #   email.should match(/^([^\s]+)((?:[-a-z0-9]+\.)+[a-z]{2,})$/i)
     #   email.should match("@example.com")
+    #   zipcode.should match_regex(/\A\d{5}(-\d{4})?\z/)
+    #   zipcode.should match_regex("90210")
     def match(expected)
       BuiltIn::Match.new(expected)
     end
 
+    alias_method :match_regex, :match
+
     # With no args, matches if any error is raised.
     # With a named error, matches only if that specific error is raised.
     # With a named error and messsage specified as a String, matches only if both match.