Merge r1835118 from trunk:

On the trunk:

 * silencing gcc uninitialized warning
 * refrainning from apr_table_addn() use since pool debug assumptions are in conflict
 * adding more assertions
 * copy-porting changes to base64 encoding code from mod_md


Submitted by: icing
Reviewed by: icing, minfrin, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1841330 13f79535-47bb-0310-9956-ffa450edef68