Implement tclPackageHook, a setup hook that adjusts TCLLIBPATH to include the
paths of any installed Tcl packages, propagates that TCLLIBPATH to
anti-dependencies, and wraps any installed binaries to set their TCLLIBPATH.
Additionally, implement a makePythonPackage-style mkDerivation wrapper to use
reasonable defaults for Tcl packages and use tclPackageHook.
