Bug 520151 - Error when modifying userPassword with proxy user
    
    https://bugzilla.redhat.com/show_bug.cgi?id=520151
    Resolves: bug 520151
    Bug description: Error when modifying userPassword with proxy user
    Fix description: The acl_access_allowed() has been modified to
    call aclplugin_preop_common() which will initialize the aclpb.
    The aclplugin_preop_common() has been modified to check for the
    ACLPB_INITIALIZED flag to avoid re-initializing aclpb.
    Reviewed by: rmeggins (and pushed by)
    (cherry picked from commit 742032c11f0dabbdc80ba204801c27c4cbe305a4)