Revision 1773069

Merge r1772919 from trunk:

mod_auth_digest: fix segfaults during shared memory exhaustion

The apr_rmm_addr_get/apr_rmm_malloc() combination did not correctly
check for a malloc failure, leading to crashes when we ran out of the
limited space provided by AuthDigestShmemSize. This patch replaces all
these calls with a helper function that performs this check.

Additionally, fix a NULL-check bug during entry garbage collection.
Submitted by: jchampion
Reviewed/backported by: jim