Project.pm: support no alternates setup
If the "noalternates" element of the project's hash has been set
to true skip the alternates setup.
Normally not used, but with this change it's now possible to use
the standard Project creation machinery to create a fork that does
not have its parent as an alternate.
This mechanism is not needed when creating a second-level repository
that does not actually have a parent fork -- alternates setup is
automatically disabled already in that case.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>