build - Update Makefile.usr to use new pkg-static

* Update to _02.  The old pkg-static doesn't understand more recent repos.

* Remove the ABIVERS prefix when ABIVERS is not manually specified,
  uname -P doesn't generate the correct results for 3.9 -> 3.10 (it
  says 4.0).

* We still allow ABIVERS to be specified in the make.