Using WT_RET/ERR_ASSERT with WT_PANIC is insufficient.

To panic the system, calling one of the WT_RET/ERR_ASSERT macros with the WT_PANIC error isn't sufficient, we need to call the underlying "panic the system" routine, wt_panic.

The best fix might be to add a WT_PANIC_ASSERT macro, and review all places we set WT_PANIC.

cc: luke.pearson