Prefer to use /dev/urandom rather than arcrandom(). I have doubts on real randomness of arc4random() in case of fork().

Rework logging.c internally, to make it easier to understand.
Document obscure functions.

stat() was never called because it was placed as a second operand
of a && operator, where the first operand is always true in normal
condition.

This commit also fixes potentials memory leaks when the log handler
cannot be created.

Export BctbxException class on Windows.

Fix build of tester on Windows.