Improve the ping_google command.

Now the command emits a dot (.) on every successful ping, and an X on a
failure. This makes it easier to get a visual representation of when and
how long the outages were.
Add a PS4 prompt value (commented by default) to ease debugging of scripts in Bash.
Added additional aliases for git-status.

Use `git stu` to see the untracked files, and `git sti` to see see
untracked as well as ignored files.
Disable visual bell.

Visual bell is when screen inverses the color of whole window. It wasn't
a problem for me, as I generally look at the keyboard while typing
commands, but the onlookers had a lot of trouble looking at those fast
visual bells.
Added a command to reset WiFi on Linux.