New runtime vrbl DOADMIN. When false, we never try to write under HKLM,

and install the Python and MS runtime DLLs into the Python dir instead of
a system dir.
Initial value is taken from new compiler vrbl _DOADMIN_ (default true),
and forced to false if the user doesn't have admin privs.
This makes it possible to *test* non-admin installs on machines where the
distinction doesn't exist (like my home box), via just changing _DOADMIN_.
It may also be useful for users who don't *want* an installer to
scribble into their system dir (for example, me(! most days)), but that
would require adding more GUI to let them get at it.