Fix up apxs editing code so that multiple invocations of apxs -a will

not result in multiple LoadModule/AddModule entries for that module;
apxs can now be used to re- enable/disable modules that were installed
using apxs.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@83447 13f79535-47bb-0310-9956-ffa450edef68