Running GCAM-USA with unconstrained water markets

[ssmithClimate]

GCAM-USA is setup by default to have water markets. If you want to run GCAM-USA with unconstrained water (e.g., an unlimited amount of water available for any uses with no resource constraints) you need to make two changes:

1. Comment out or delete this line in the configuration.xml:
   <Value name = "water_supply">../input/gcamdata/xml/water_supply_constrained.xml</Value>

2. Make a copy of this input file:
   ../input/gcamdata/xml/water_td_USA.xml
   and delete all the resource sectors at the end of this file that start with <resource name=....
   Use this edited file as an input instead the original water_td_USA.xml.

What is happening is that this section of the input is deleting energy inputs from sectors that don't exist in GCAM-USA, but as a result this ends up creating an empty resource object, which causes a crash. (Thanks @pkyle for the tip!).