Move *_DECLARE_* macros to beginning of line in headers. Patch submitted by: normw gknw net.

mod_proxy: Move ap_proxy_strmatch_path and ap_proxy_strmatch_domain out of the public API.

mod_proxy: Make the ap_proxy_is* functions private.

mod_proxy: Make ap_proxy_retry_worker() into an optional function. Allows mod_lbmethod_bybusyness, mod_lbmethod_byrequests, mod_lbmethod_bytraffic and mod_lbmethod_heartbeat to be loaded without mod_proxy yet being present, which happens when modules are loaded in alphabetical order.