Merged in some non-Sitecore 7 changes from the sitecore-v7 branch so that Paul can make additional changes to the CanonicalUrl class.
Revised to use HtmlTextWriter instead of just output, and to exit if there is no context item.
Merge pull request #7 from ptiemann/CanonicalURL

Revised to use HtmlTextWriter instead of just output, and to exit if the...
Merge branch 'master' into sitecore-v7

Conflicts:
	src/pixelmedia.sitecorecms.controls/Controls/CanonicalUrl.cs
	src/pixelmedia.sitecorecms.controls/PixelMEDIA.SitecoreCMS.Controls.csproj