Private module imports take precedence

For module Needs imports, give private module exports a
higher priority than runtime library (lib) imports. Doesn't
affect scripts, which use strict in-order precedence already.

See http://issue.cc/r3/1998 for details.
Fix crash in RESOLVE/extend/only

Ensure that the internal helper function Expand_Frame properly
terminates the frame's word and value series, even when _not_ copying
from the original frame.

The /extend part of RESOLVE is currently the only user of non-copying
Expand_Frame. Without proper termination, the code in RESOLVE makes
invalid memory accesses at (or past) the frame's tail, causing crashes.

This fixes CureCode issue #2017.
Merge pull request rebol/r3#114 (BrianHawley/fix-1998-private-module-precedence) into community

* BrianHawley/fix-1998-private-module-precedence:
  Private module imports take precedence
Merge pull request rebol/r3#115 (earl/fix-2017-resolve) into community

* earl/fix-2017-resolve:
  Fix crash in RESOLVE/extend/only