Merge r1750043 from trunk:

Replace the proxy_mods_enable logic, with its hazardous 'yes' value that
aborts the build on missing dependencies, with a local override of the
module_selection as 'most', and module_default of the same shared|static
model that was requested through --enable-proxy.

[For trunk, we need to reevaluate the 'most' condition of some of the more
esoteric modules, and simply drop the module_default override; where a user
wants to enable -only- mod_proxy, plus one proxy mechanism, the legacy 2.4.x
behavior retained by this patch is nuts. For one example,
  --enable-modules=few --enable-proxy-yes --enable-proxy_http
is a completely specific and legitimate syntax --- adding 10 other proxy
providers in response to this syntax is absurd.]


Submitted by: wrowe
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1750483 13f79535-47bb-0310-9956-ffa450edef68