MSVC 2008/2010 Projects: Add "Install" Project

This adds "install" projects for the Visual Studio 2008 and 2010 projects,
so that the build results will be copied to a common directory where the
dependent DLLs are, which will ease testing and packaging.

* MSVC_2008/gtkmm-install.vsprops:
* MSVC_2008/install.vcproj:
* MSVC_2010/gtkmm-install.props:
* MSVC_2010/install.vcxproj: Add project files and property sheets to be
  used to copy the build results to a common directory, where the
  dependencies reside in.
* MSVC_2008/gtkmm.sln:
* MSVC_2010/gtkmm.sln: Include the "install" project in the build process.
* MSVC_2008/filelist.am:
* MSVC_2010/filelist.am: Include the added project files and property
  sheets in the dist.