1401 and NVIDIA driver 2.4.3

• Fix a desktop freeze followed by a kernel panic ("thread_call group 'high' reached max thread cap") a few seconds to a few minutes after logging in (#295). The display driver started a new kernel thread for every vblank and every cursor move while an earlier one was still waiting; each of its callbacks now runs one at a time.
• Metal apps translate a shader they have already seen without hashing it again: the digest kept on the translated text was never reused (PR #294, thanks watchthelight).