Merge r1493921, r1515162 from trunk:

mod_socache_shmcb.c: Remove arbitrary restriction on shared memory size
previously limited to 64MB.


Limit SHMCB_MAX_SIZE to min(UINT_MAX, APR_SIZE_MAX) to match the current code

Submitted by: minfrin, sf
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1551932 13f79535-47bb-0310-9956-ffa450edef68