Tie up memory module tests

- Re-organize wp_memory.w tests
- Remove redundant header section which broke calls to the memory test
  suite
- Add WP_TEST_THROW definition to wp_test.h (due to a possible
  shortcoming with CWEB)
- Add @<Register Tests@> section, which will be renamed later
- Change WP_TEST_LOG calls in wp_memory.w to new(er) WP_TEST_FAIL calls
  (deprecated)
- Remove references to wp_test_t type (deprecated)
- Remove references to WP_TEST_CALL (deprecated)
- Add additional (required) includes in wp_memory_tests.c
- Add wp_memory_tests.c to tegen_SOURCES in Makefile.am