Fix mod_so handling. Basically, if --enable-so or --enable-some-module=shared is specified on the ./configure line, then mod_so is included in the build, -ldl is added to LIBS, and --enable-dso is added to APR's configure line. Otherwise, mod_so is turned off, -ldl is not added, and APR is specifically told to build without DSO support.
httpd/httpd/trunk/acinclude.m4
httpd/httpd/trunk/modules/aaa/config.m4