Check if the binary still exists when doing a /RESTART

[wilmer]

I just tried to revert a BitlBee binary, but accidentally messed up the symlinks to the current binary which took down the ForkDaemon. It blindly tries to execve() itself, but it'd probably be nice if it could first check if the binary still exists.

Surely there's a race condition here, etc etc, but it's not *that* important.

To fix this completely, I may try to fall back to a call back to main() if the exec() fails.

[dx]

HI WILMER :D. HAVE A WONTFIX!

Really though this doesn't seem like something worth fixing. You broke it, it broke as a result, nobody is surprised.