updated for version 7.4.299
Problem:    When running configure twice DYNAMIC_PYTHON_DLL may become empty.
Solution:   Use AC_CACHE_VAL. (Ken Takata)
Added tag v7-4-299 for changeset daebf8ce6608
updated for version 7.4.300
Problem:    The way config.cache is removed doesn't always work.
Solution:   Always remove config.cache. (Ken Takata)
Added tag v7-4-300 for changeset 1157079ca5f1