Big mod_lua backport:

r1201460: Add some todos from apachecon notes.
          Submitted by: covener

r1351012: Change prototype of vm_construct, to work around gcc bug which
          causes a segfault.  PR: 52779
          Submitted by: Dick Snippe <Dick Snippe tech omroep nl>

r1351013: Allow tail call optimization in log methods, remove foo method.
          Submitted by: sf

r1351014: Add a few missing request_rec fields. Rename remote_ip to
          client_ip to match conn_rec.
          Submitted by: sf

r1351017: Change various strings from char * to const char *.
          Submitted by: sf

r1351018: Factor common code into utility function.
          Also improve logging a bit and adjust some log levels.
          Submitted by: sf

r1351019: Use macro to make definition of integer fields more compact.
          Submitted by: sf

Reviewed by: humbedooh, covener, sf
Backported by: humbedooh, rjung


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1369494 13f79535-47bb-0310-9956-ffa450edef68