Speed up ap_md5digest() a little.

* util_md5.c (ap_md5digest): Use a larger buffer; ensure size is a
multiple of 64 to prevent buffering in MD5 code.  Remove redundant
'length' variable.  Reset read size in case of short reads.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@100672 13f79535-47bb-0310-9956-ffa450edef68