Make sure that we don't destroy the current CONFIG

Found this by looking at other example rebar.config.script examples. We
want to be sure we aren't accidentally removing configuration values
from the global CONIFG value.
Check for configure settings to enable cURL
Ignore built files
Switch JSON encoding/decoding to Jiffy
Switch the default URI port to 15986

BigCouch has the single node API on 15986 for node 1. This is just a
temporary convenience change while we hack on the merge.
No longer use conditional imports for main.c

Dropping support for versions of SpiderMonkey other than 1.8.5 means we
don't need to bother with the conditional import.
Add dbs and nodes to the system dbs lists

These are the internal database names used by BigCouch for storing
cluster information.
Make sure and save the default referer
Update license headers