Fix typo (spotted by cscott)
Route Spacebars errors properly

Now Spacebars syntax errors (as well as html_scanner errors) go through proper error reporting channels rather than throwing exceptions.  For simple cases, we are back to showing nice errors like Handlebars did on devel, with context.

Next:  Comb the spacebars compiler for errors that are thrown or lack good line numbers.  Go through our own list of bad error messages.