Bash: update mrsync alias

Incorporates (some) of the latest features we've learned from creating
the `rsynclive` script.
Git: update template to allow commit msg headers up to 72 chars

This is an increase from the previous 50 char limit, and reflects the
latest Linux kernel git repo patch guidelines (which give a hard limit
of 70-75 characters, and a suggested limit of 50 chars.)
Bash: alias `g` to `git`
Bash: add `histup` alias to update current term's history buffer
Git: add `diet` command to try to recover disk space from large repos