assuan: Use exponential decay for first 1s of spinlock.

assuan: Use exponential decay for first 1s of spinlock.

* common/asshelp.c (wait_for_sock): instead of checking the socket
every second, we check 10 times in the first second (with exponential
decay).
--

This cuts the wall clock time for the standard test suite roughly by
half.

GnuPG-bug-id: 3490
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
(cherry picked from commit 149041b0b917f4298239fe18b5ebd5ead71584a6)

Gbp-Pq: Topic from-master
Gbp-Pq: Name assuan-Use-exponential-decay-for-first-1s-of-spinlock.patch