interp.test

- nsf.c: * change mem-count statistics from per-interp to per-thread * generalized GetObjectFromCmdTable() to ReverseLookupCmdFromCmdTable() * changed GetObjectScreenedByCmdName() to GetHiddenObjectFromCmd() * modularized interp.test to locate potential problems faster * partly simplified interp.test syntactically * deacivated a few tests in interp.test for the time being (runs commands after finalize)

- generic/nsf.c: After several takes, adding support for basic handling of hidden and re-exposed objects in the sense of [interp hidden|hide|expose]. I wanted to make sure that NSF does not crash upon basic hiding/exposing operations (see tests/interp.test) and guarantees that hidden/re-exposed objects are properly handled when cleaning up object systems, i.e., the destructors are called and physical deletion is performed. [interp hidden|hide|expose] is challenging for NSF (as well as TclOO) because they way it is implementing effectively modifyies command names *without* providing any calling back to trace these changes (as for renames). As a consequence, object and command names start to diverge once an object has been hidden or re-exposed. As the changes affect the cleanup machinery in ObjectSystemsCleanup() & friends, I verified for leaks by running valgrind; no leaks were found running destroy.test and interp.test. - tests/interp.test: A test suite that covers basic scenarios of hiding and exposing objects. - Makefile.in: Registering interp.test with make env