Add assertions that capture invalid configurations for new libraries.

Fix current findings, which should fix cases of NO_SHARED not building
properly.

Given libfoo:

• Ensure that a LIBFOO is set. For INTERNALLIBS advise setting this in src.libnames.mk, otherwise bsd.libnames.mk.
• Ensure that a LIBFOODIR is properly set.
• Ensure that _DP_foo is set and matches the LIBADD in the build of foo's own Makefile

Sponsored by: EMC / Isilon Storage Division