Port configure script to Node, step 2: build JS tests.

This is step 2 of porting our configure script to Node.  This version improves
on the previous by directly linking all source files to avoid needing to
recompile when writing/running tests.

Progress on #7.
Merge pull request #195 from nicksay/build-with-node-2

Port configure script to Node, step 2: build JS tests.