to 1 it automatically disables use of the bias since that is almost certainly
what the user will want to do.

instead of rolling its own implementation.

icon files.

avoid some silly warnings from gcc 4.4 and 4.5.

unlock a dlib::mutex it doesn't own.  This is technically a non-backwards
compatible change to the API but it has always been implemented in a way that
didn't allow this kind of double unlock() on non-Windows platforms.
Additionally, the recent change to the dlib::mutex implementation on windows
also no longer allows this kind of double unlock.

instead of mutex::unlock().

of a "mutex" (i.e. the thing made by CreateMutex()) since a critical section does the
same thing but faster.

function objects.  In general, I noted that in most cases they are safe to use
from multiple threads so long as they are not modified.