Allows SMF method to override Apache binary to start and thus select if
we want prefork/worker Apache MPM.

--- support/apachectl.in	Tue Jul 11 20:38:44 2006
+++ support/apachectl.in	Tue May 14 07:40:03 2013
@@ -41,7 +41,7 @@
 # --------------------                              --------------------
 # 
 # the path to your httpd binary, including options if necessary
-HTTPD='@exp_sbindir@/@progname@'
+HTTPD=${HTTPD:-@exp_sbindir@/@progname@}
 #
 # pick up any necessary environment variables
 if test -f @exp_sbindir@/envvars; then