Fix the build on Windows

Collateral damage: readdir_r isn't present in mingw, but bad old readdir
is fine for how we are using it.
Merge pull request #83 from mccoyst/windows

Fix the build on Windows
Zero the enemy struct before scanning.

Otherwise some of the fields may be nonesense.  How did this ever work?

Fixes #15
Merge pull request #85 from eaburns/dev/eaburns

Zero the enemy struct before scanning.