Merge r1749659, r1749678 from trunk:

Merge r1749659, r1749678 from trunk:

Simplify, and correct the dependency handling of mod_proxy_hcheck

Cause missing mod_watchdog to 'unset' the --enable-proxy default, rather than
disable the module. This forces the module logic to emit a warning of the
missing dependency; changes the output from

checking whether to enable mod_proxy_hcheck... no

to

configure: WARNING: "mod_watchdog is disabled but required for mod_proxy_hcheck"
checking whether to enable mod_proxy_hcheck... no (disabled)

Submitted by: wrowe
Reviewed/backported by: jim

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1749774 13f79535-47bb-0310-9956-ffa450edef68