detecting whether an argument in a callback to R uses local variables. If it doesn't, we just leave the expression as is. This allows us to refer to R variables and also complex objects  specified in the 'template' call.  Also, we insert the actual template call into the module iff the .ee argument is enabled in compileFunction. This is a good thing.
more documentation and switch to env[['.ExecEngine']] rather than .ee argument in case it is set as a side effect during compilation