ab: Check and handle POLLOUT before POLLIN. #421

Job	Run time
Empty APLOGNO() test	43s
Default	3m 55s
All-static modules	5m 6s
Prefork MPM, all-modules (except cgid)	4m 38s
Worker MPM, all-modules	4m 44s
Shared MPMs, all-modules	4m 36s
Event MPM, all-modules, mod_cgid only	5m 58s
Event MPM, all-modules, no CMSG_DATA	4m 41s
Default, all-modules + install	4m 49s
Default, all-modules, random test order	5m 12s
GCC 10 maintainer-mode w/-Werror, install + VPATH	4m 55s
All-modules, APR 1.7.4, APR-util 1.6.3	4m 34s
APR 1.8.x, APR-util 1.7.x	6m 39s
Pool-debug	7m 44s
Shared MPMs (event), pool-debug, SSL/TLS variants	11m 0s
Shared MPMs (worker), pool-debug, SSL/TLS variants	10m 31s
Shared MPMs (prefork), pool-debug, SSL/TLS variants	11m 16s
litmus WebDAV tests	2m 32s
Regenerate ap_expr	5m 21s
APR 1.7.4, APR-util 1.6.3, LDAP	5m 27s
APR trunk thread debugging	5m 2s
UBSan	5m 27s
ASan	7m 36s
ASan, pool-debug	8m 11s
HTTP/2 test suite	12m 52s
MOD_TLS test suite	6m 5s
	2h 39m 34s

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