Fixes "options bleed", aka. CVE-2017-9798:

  https://nvd.nist.gov/vuln/detail/CVE-2017-9798
  https://blog.fuzzing-project.org/60-Optionsbleed-HTTP-OPTIONS-method-can-leak-Apaches-server-memory.html

From <https://svn.apache.org/viewvc/httpd/httpd/branches/2.4.x/server/core.c?r1=1805223&r2=1807754&pathrev=1807754&view=patch>.

--- a/server/core.c	2017/08/16 16:50:29	1805223
+++ b/server/core.c	2017/09/08 13:13:11	1807754
@@ -2266,6 +2266,12 @@
             /* method has not been registered yet, but resource restriction
              * is always checked before method handling, so register it.
              */
+            if (cmd->pool == cmd->temp_pool) {
+                /* In .htaccess, we can't globally register new methods. */
+                return apr_psprintf(cmd->pool, "Could not register method '%s' "
+                                   "for %s from .htaccess configuration",
+                                    method, cmd->cmd->name);
+            }
             methnum = ap_method_register(cmd->pool,
                                          apr_pstrdup(cmd->pool, method));
         }
