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

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.