Added support for following links containing only an image via it's alt-attribute

Given the following HTML:
<a href="/foo"><img src="img.jpg" alt="Img alt text" /><a/>

@session.click_link("Img alt text") will now work and follow to "/foo"

lib/capybara/xpath.rb

@@ -56,8 +56,8 @@ module Capybara
     end
 
     def link(locator)
-      xpath = append("//a[@href][@id=#{s(locator)} or contains(.,#{s(locator)}) or contains(@title,#{s(locator)})]")
+      xpath = append("//a[@href][@id=#{s(locator)} or contains(.,#{s(locator)}) or contains(@title,#{s(locator)}) or img[contains(@alt,#{s(locator)})]]")
-      xpath.prepend("//a[@href][text()=#{s(locator)} or @title=#{s(locator)}]")
+      xpath.prepend("//a[@href][text()=#{s(locator)} or @title=#{s(locator)} or img[@alt=#{s(locator)}]]")
     end
 
     def button(locator)

spec/dsl/click_link_spec.rb

@@ -46,6 +46,23 @@ module ClickLinkSpec
         end
       end
 
+      context "with alternative text given to a contained image" do
+        it "should take user to the linked page" do
+          @session.click_link('awesome image')
+          @session.body.should include('Bar')
+        end
+
+        it "should take user to the linked page" do
+          @session.click_link('some imag')
+          @session.body.should include('Bar')
+        end
+
+        it "should prefer exact matches over partial matches" do
+          @session.click_link('fine image')
+          @session.body.should include('Bar')
+        end
+      end
+
       context "with a locator that doesn't exist" do
         it "should raise an error" do
           running do

spec/views/with_html.erb

@@ -6,6 +6,7 @@
   et dolore magna aliqua. Ut enim ad minim veniam,
   quis nostrud exercitation <a href="/foo" id="foo">ullamco</a> laboris nisi
   ut aliquip ex ea commodo consequat.
+  <a href="/with_simple_html"><img src="http://www.foobar.sun/dummy_image.jpg" width="20" height="20" alt="awesome image" /></a>
 </p>
 
 <p id="second">
@@ -25,6 +26,8 @@
   <a href="/with_simple_html#anchor">Anchor on different page</a>
   <a href="/with_html#anchor">Anchor on same page</a>
   <input type="text" value="" id="test_field">
+  <a href="/redirect"><img src="http://www.foobar.sun/dummy_image.jpg" width="20" height="20" alt="very fine image" /></a>
+  <a href="/with_simple_html"><img src="http://www.foobar.sun/dummy_image.jpg" width="20" height="20" alt="fine image" /></a>
 </p>
 
 <div id="hidden" style="display:none;">