Nicer debug printing when op doesn't have an associated source line
Avoid incorrect heap addressing when retrieving a symbol's address
Bug fix: was not properly initializing the default values of output
params if they were written but never read. Most of the time, the output
param was written over in the shader body anyway, so this was not
noticed.  But in cases where it might not be assigned in the main shader
body, the default value was not present.