mod_lua: Sync 2.4.x with trunk (more or less); Backport a fix and some code harmonization:

- IVM changed to use shm
- More verbose error logging (no functional change)
- Miscellaneous refactoring that was in trunk but not in 2.4.x (no functional change as such)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1604339 13f79535-47bb-0310-9956-ffa450edef68