__fish_print_packages: correct syntax for yum, improve yum/rpm pipelines

Closes #1269 (output to cache file).

Reworks the editing pipeline for both yum and rpm completions down to a
single sed command.
sshfs completions: use all directories as mount points

Closes #1268.
Experimental option to build in a static ncurses library with its own terminfo, eliminating system dependency.