Fix install path for framework to use @rpath

This commit is a fix to the framework install path. Specifically the change is in the build settings' "Installation Directory" to use @rpath instead of @loader_path/../Frameworks. As of 10.5 or later, @rpath should be the default for all frameworks, as it allows the loading code to specify path information to correctly resolve the location instead of hard coding it relative to the loading binary path. This is important when you have a framework inside of an application which is using the destination framework. (ex: MyApp->MyAppGraphics.Framework->CorePlot.Framework)

Reference website with great explanation on why this change should be made:

http://www.dribin.org/dave/blog/archives/2009/11/15/rpath/