Little tweaks. Some concatenations are still erroneously quoted, but that can be easily worked around for the time being with the 'unquote' built-in.

Redoing the arithmetic. Should fix some erroneous behavior on complex expressions in weird contexts.

Conflicts:
	functions.cpp

Eh, not doing the cloning thing after all. If there's an error in the argument to a built-in function, just report the entire call site rather than the location of the argument.

Cloning values fetched from variables in order to set their paths and line-numbers to the point of reference. (Using the original values would result in paths and line-numbers being reported as the point of assignment, which is not helpful for debugging.)

Passing the path and line-number into the built-in functions in order to generate the most accurate file-names and line numbers for intermediate return values.

Using the file-name and line-number of the function name as the file-name and line-number of a function call.