Exceptions stacktrace

[kaol]

This code adds exception handling to template loading. I'm afraid runNode got uglier by this change, I had to make sure that the consolidate evaluation happens already there. By the time the consolidate in compileTemplate would get run the context would already have been lost. I'm not sure whether this causes the pure bytestrings to be created twice.

callTemplate didn't seem right with its lacking _curTemplateFile manipulation and I added it as another patch in this branch.

[mightybyte]

Can you briefly summarize the main motivation for this? Adding contextNode to SpliceError makes perfect sense to me. But I don't quite understand how that relates to the exception stuff that was added.

Also, the Travis build failures need to be fixed before I can merge.

[mightybyte]

Can you add to this comment something like "Since this is compiled splice mode, runNode gets executed at load time so exceptions are ok"?

[mightybyte]

Ok, I understand now. You're trying to provide better error messages when user splice code throws an exception. Using Either String instead of exceptions for this would be a large change because it would impact user-written splice code. Exceptions shouldn't be a problem here because the compiled splice runNode gets executed at load time. And, we already call error in here.

We could just eat the exception, create a SpliceError, and not re-throw. This would allow the user to see more errors at a time without having to fix some and then re-run. But this distinction probably won't be a big deal in practice, so I'm fine with either way.