Use CTest to simplify testing options

Use CTest to simplify testing options
Add CMake variable TEST_STOCK_ZLIB to disable some tests if attempting
to run our testsuite on stock zlib.
PR depends on CMP0077, introduced by CMake 3.13.
Upped minimum compatible CMake version to 3.13, same as we have
actually been telling people was the minumum for years on the wiki.
Upped upper compatible CMake version to 3.31, my current version.