Disable darkroom by default when darkgray is off by default

The darkroom option tends to look really awful on Windows due to its
inability to display dark gray, turning virtually everything not in
immediately line of sight an ugly dark blue instead.
Bump patchlevel to 0.5.1

The `dynahack-0.5.0-win.zip` archive bundled compiled level files whose
version mismatched with the game actual, causing it to freak out and not
touch them, instead creating generic maze levels.

This packaging error is due to some sort of shortcoming in the way
Daniel Thaler asked CMake to compile level files (which was not amended
by changes made in NetHack4), causing them to fail to either be
recompiled individually or repackaged into `nhdat`.  This is a serious
bug that has laid dormant in the build system for a long time.

In the meantime, release builds should always be made with fresh `build`
and `install` directories.