The GUID of the "Install" project files happen to be the same as Pango's
"install" projects, so we need to update the GUID here so that the projects
can cooperate with each other when used in an all-in-one build for the GTK+
stack.
Rename the install projects as gtk-install, to ease the integration of the
projects in a grand solution that may be used to build, for example, the
entire GTK+ stack.