Changed slassoc.c to use explicit ref counting instead of MMTs.
Changed sllist.c to use explict reference counting.
Updated json-module to use modified API.  Fixed some leaks.
Reverted src/test/Makefile and updated list, assoc tests.  Added API tests to sltest.c.
Updated sltest.c to be independent of inc.c.
merging JED's branch 'test' into Mh's branch 'patches'
extracted API test for {Assoc|List}_Type from sltest.c to {assoc|list}.c
& added tests showing that pushing and popping (or vice versa) gives the same value