r3539: much nicer async open delay code.

r3539: much nicer async open delay code.

The previous code didn't handle the case where the file got renamed or
deleted while waiting for the sharing violation delay. To handle this
we need to make the 2nd open a full open call, including the name
resolve call etc. Luckily this simplifies the logic.

I also expanded the RAW-MUX test to include the case where we do
open/open/open/close/close, with the 3rd open async, and that open
gets retried after both the first close and the 2nd close, with the
first retry failing and the 2nd retry working. The tests the "async
reply after a async reply" logic in pvfs_open().