Fix a spelling typo in a comment
Update to get meta data for postgresql plugin

collectd v5.0 starts putting the meta data in a different place with the
write_httpd plugin.
Update database creation script

Use a here script to for a COMMIT in case autocommit is disabled.
Update json-c requirement note

json-c 0.9 had a bug when converting JSON arrays of integers to strings.
The 0.10 release seems to have corrected that.
Handle case when request_method is NULL