fixes #542 Do not try to use a descriptor whose size is 0 - assume it's
for an internal dictionary and default to interpreting the key as a string
fixes #530

SERVER-8515 avoid memory corruption by checking max file descriptor limit
fixes #529 Remove temp collection cleanup. Temp collections should
always be rolled back by a failing transaction or manually cleaned up
by a committing transaction. By not opening all databases on startup,
we prevent a bug where to many open file descriptors breaks the
socket listening code in initAndListen(), see SERVER-8515