add scp path to _PATH_STDPATH

[Kevin Steves]

On Wed, 28 Feb 2001, Tim Rice wrote:
: > i don't like munging path if a user specified a path
:
: Then you still have the same problem of scp not working.
: Configure does give ample warning when it modifies the path.
: I figure if someone REALLY wants a path that doesn't iclude the location
: of scp they can edit config.h after configure runs.

i still believe --with-default-path= should *not* be modified.  the
default settings should work (today they don't) and if a user chooses to
override them we shouldn't assume to know more than they do.  if we
want, we can display warning message for this case.