First check for exact filename when dynamically loading C lib
Add the RTLD_GLOBAL option to dlopen

This enables libraries that depend on other libraries to be openable by making
the symbols of loaded libraries globally available.
Added isNull emulation plus another primitive
More primitives
Fixed semantics of isNull emulation to properly wrap in IO
Look in the environment before the definitions in executor
Merge pull request #300 from david-christiansen/providers

Providers