Initial attempt at a port of USM onto POSIX sh.

I haven't yet tested on anything except /bin/dash available on
Ubuntu 14.04.1, but it appears to work there currently.
Fixed an issue with the ~/.usm-env script template.

Ubuntu's /bin/sh was choking on the use of `>&` - I replaced this with
the `-s -q` flags for grep, and the script is sourced properly.
Fixed `usm ls` to print out things in order.

Previously, `usm ls` would print out software in reverse order.
Merge remote-tracking branch 'origin-write/master'