The render code path in `template_file` was doing unsynchronized access
to a shared mapping of functions in `config.Func`.
This caused a race condition that was most often triggered when a
`template_file` had a `count` of more than one, and expressed itself as
a panic in the plugin followed by a cascade of "unexpected EOF" errors
through the plugin system.
Here, we simply turn the FuncMap from shared state into a generated
value, which avoids the race. We do more re-initialization of the data
structure, but the performance implications are minimal, and we can
always revisit with a perf pass later now that the race is fixed.
This is REALLY heavy and would be really hard to maintain any sort
of compatibility with, but it is what we're going to do during dev
initially (if we don't ship with it) in order to just get stuff working.
Paul Hinze