[reSIProcate] Log pthread_key_t

[david Butcher]

There was probably an issue with initializing the pthread_key_t
mLevelKey in Log. I was unable to reproduce the issue, but it looked
like (and was reported that) Bad Things could happen when logging
preceded Log::initialize for *nix. The fix uses a header triggered
init() coupled with a typical static init ternary idiom.

Committed revision 5306.

Let me know if issues (re)appear.

david