mod_proxy: restore reuse of ProxyRemote connections when possible. #1334

Job	Run time
Empty APLOGNO() test	34s
Default	3m 52s
All-static modules	4m 35s
Prefork MPM, all-modules (except cgid)	4m 12s
Worker MPM, all-modules	4m 30s
Shared MPMs, all-modules	4m 43s
Shared MPMs, all-modules, 64-bit ARM	7m 28s
Event MPM, all-modules, mod_cgid only	4m 17s
Event MPM, all-modules, no CMSG_DATA	5m 23s
Default, all-modules + install	4m 38s
Default, all-modules, random test order	4m 26s
GCC 12 maintainer-mode w/-Werror, install + VPATH	3m 51s
All-modules, APR 1.7.6, APR-util 1.6.3	4m 20s
APR 1.8.x, APR-util 1.7.x	5m 58s
Pool-debug	7m 2s
Shared MPMs (event), pool-debug, SSL/TLS variants	9m 34s
Shared MPMs (worker), pool-debug, SSL/TLS variants	9m 38s
Shared MPMs (prefork), pool-debug, SSL/TLS variants	9m 7s
litmus WebDAV tests	2m 20s
litmus WebDAV tests, APR trunk, LMDB	3m 3s
Regenerate ap_expr	4m 18s
APR 1.7.6, APR-util 1.6.3, LDAP	4m 6s
APR 1.7.x, APR-util 1.7.x, LDAP	5m 45s
APR trunk thread debugging	4m 39s
UBSan	4m 59s
ASan	6m 59s
ASan, pool-debug	7m 21s
HTTP/2 test suite	6m 46s
Configured w/reduced exports	2m 18s
OpenSSL 3.1	3m 44s
OpenSSL 3.4 -Werror	4m 28s
OpenSSL 3.4 no-engine	3m 43s
OpenSSL 3.5 no-engine -Werror	5m 5s
	2h 47m 42s

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