A quick heads up to everyone migrating solutions from SharePoint 2010 to 2013: the days of manual labor are over!
Most posts on the Net still show the old way of upgrading. This was done by manually editing .csprj and manifest.xml files, doing a global search and replace from “14.0.0” to “15.0.0”, and so on.
Thanks to an update from 2013-02-26 for Microsoft Office Developer Tools for Visual Studio 2012 this will now all happen automaticallly when you open a SharePoint 2010 solution in Visual Studio 2012. See External References for details.
For our solution we didn’t even have to update the _layouts folder path – everything just worked.