Add spec for finding inputs by alt text

Rakefile

@@ -56,7 +56,7 @@ end
 
 require 'spec/rake/verify_rcov'
 RCov::VerifyTask.new(:verify_rcov => :rcov) do |t|
-  t.threshold = 97.2 # Make sure you have rcov 0.7 or higher!
+  t.threshold = 97.3 # Make sure you have rcov 0.7 or higher!
 end
 
 remove_task "default"

spec/api/clicks_button_spec.rb

@@ -332,6 +332,16 @@ describe "clicks_button" do
     @session.expects(:get)
     @session.clicks_button
   end
+  
+  it "should find image buttons by their alt text" do
+    @session.response_body = <<-EOS
+      <form action="/">
+        <input type="image" alt="Go" />
+      </form>
+    EOS
+    @session.expects(:get)
+    @session.clicks_button "Go"
+  end
 
   it "should recognize button tags by content" do
     @session.response_body = <<-EOS