Add zipinfo & zipgrep to SDK

Fixes #465 (closed). This MR is totally untested, though I have verified that unzip is indeed built with zipinfo support by creating a symlink in /tmp locally.

(I don't really understand why this recipe open-codes the files to install, rather than running make -f unix/Makefile with MANDIR and BINDIR set appropriately. What's wrong with the makefile? I assume it was done this way for a reason so I've followed that, but perhaps not.)