Adding conditionals and refactored _resolve to be much more clear and easy to update

Hello sho, eford, jon, 

Please review the following commits I made in branch 'jeremy-conditionals'.

8b267e70bf720547a4d3f5884100214116681986 (2013-02-25 22:25:51 -0800)
Adding initial conditionals test syntax
Adding a few internal nodes

Adding ignoredErrors functionality

Test of if-like logic in place

Latest conditionals stuff

Changing conditionals to use guards

Merged 2 branches

Working on conditionals

Trying to get back to a working state

Trying to get back to a working state

yay

Adding ConditionalError

throwing conditional errors

Errors pass through

else works again

Better conditional test

test without else

Adding test with a syntax error

++comments

++comments

++comments

Refactoring resolver to be more readable / extensible

Working on new resolver

Fixed error handling for subgraphs and literals

Fixing conditionals

++comments

rewritten resolver works

Rearranged comments

Added new disableCache test

R=sho
R=eford
R=jon