Upgrade disco to 0.4.5 and fix Python installation paths

Disco 0.3.2 was not building. This addresses it by jumping to a new version.
* Upgrades disco to version 0.4.5.
* Breaks the discodex project out to a separate formula, corresponding
to its reorganization opn GitHub.
* Fixes Python installation paths by passing PY_INSTALL_OPTS through the
Makefile.
* Switches from inreplace() to a patch.
* Uses the official discoproject download instead of the tuulos fork.