fix segfault when cleaning up MixChunks on windows

We built the libSDL binaries several years ago, and so it was built
against an older runtime library (msvcrt.dll).
Now we build SDL itself against msvcr110.dll for example, and therefore
allocate on another heap than the free() is taking place, which happens
in libSDL_mixer itself.
See: http://stackoverflow.com/questions/23257226/sdl-mixer-mix-freechunk-crashing-on-sample-created-in-memory
dev release 2.543_1
updated Alien::SDL's version to get an OpenBSD/pthread fix, dev release 2.543_2
fix required version of dependency Alien::SDL
another attempt to correctly update dependency version of Alien::SDL
release 2.544
TestTool::init: properly handle SDL::init errors

So far TestTool::init was just capturing stdout and stderr of SDL::init,
using stderr to check whether SDL::init failed. This, other than being
fragile, misses the init errors.

Switch from checking stderr to checking the actual result code of
SDL::init.