OS/2: AP_MPM_WANT_SET_MAX_MEM_FREE needs to be defined for ap_max_mem_free to

be available which is required for the recent bucket_alloc changes.

Backport of r1.6 build fix.
Reviewed by: jwoolley


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@101201 13f79535-47bb-0310-9956-ffa450edef68