1.0.19.15: package name conflict patched from Michael Weber

1.0.19.15: package name conflict patched from Michael Weber

 * Tests for package system name conflict resolution.

 * Fixed EXPORT bug which left symbol unexported in conflict
   situations.

 * Unbreak RESOLVE-CONFLICT restart:
    ** USEing packages with conflicting symbols
    ** Correctly handle conflicts involving CL:NIL by passing (list
       symbol) to package frobbing functions which take a list
       designator.

 * Removed commented-out version of NAME-CONFLICT.