Output the backtrace like Rails does, so list the name and version of…

… the gem before it's file path. Adds the enhancement requested in #29.

lib/better_errors/stack_frame.rb

@@ -50,7 +50,7 @@ def gem?
     def gem_path
       Gem.path.each do |path|
         if filename.index(path) == 0
-          return filename.gsub("#{path}/gems/", "(gem) ")
+          return filename.gsub(%r{#{path}/gems/([^/]+)-([\w.]+)/}, '\1 (\2) ')
         end
       end
     end

spec/better_errors/stack_frame_spec.rb

@@ -54,15 +54,15 @@ module BetterErrors
         Gem.stub!(:path).and_return(["/abc/xyz"])
         frame = StackFrame.new("/abc/xyz/gems/whatever-1.2.3/lib/whatever.rb", 123, "foo")
 
-        frame.gem_path.should == "(gem) whatever-1.2.3/lib/whatever.rb"
+        frame.gem_path.should == "whatever (1.2.3) lib/whatever.rb"
       end
 
       it "should prioritize gem path over application path" do
         BetterErrors.stub!(:application_root).and_return("/abc/xyz")
         Gem.stub!(:path).and_return(["/abc/xyz/vendor"])
         frame = StackFrame.new("/abc/xyz/vendor/gems/whatever-1.2.3/lib/whatever.rb", 123, "foo")
 
-        frame.gem_path.should == "(gem) whatever-1.2.3/lib/whatever.rb"
+        frame.gem_path.should == "whatever (1.2.3) lib/whatever.rb"
       end
     end