#21 Resolve DSO functions at compile time.

[Paul Gregory]

Currently, any functions not found at compile time are
presumed to be in DSO's, and will be resolved at
runtime. This means it is impossible to do typechecking
(and any required casting) at compile time, forcing the
SL coder to be explicit about any return types and
argument casting.

It would be useful to search in the "include"
searchpath for any possible DSO candidates at compile
time to resolve the function call and allow better
handling of type casting.