sandbox: various potion merges, make test uses now runtests.sh

* test: replace test with test/runtests.sh -q
  also use +$(MAKE) to pass jobserver info to runtests.sh
* sandbox build: strip PLIBS from .a sources
* sandbox: adjust make test target for SANDBOX=1
* test/runtests.sh: skip SANDBOX tests
* sandbox: move initializers to main(),
    explicit PLIBS_OBJS static targets, esp. for SANDBOX
    TODO: the initializers decl and call should be generated
    into config.h