Allow ~/.personal/ to contain personal override scripts

[benknoble]

Any executable file in that directory will be sourced as a way to override defaults or create other personalizations. This prevents dreaded merge conflicts when updating this repo, and allows you to VCS your own personalization scripts, since they live in their own directory.

1. Files must be executable to allow the inclusion of README's or other files in the directory.
2. This currently doesn't allow a personal e.g. .inputrc for customizing that (but you can use bind in a script to interact with the readline library!)
3. Best current usage of this is alias/function defs, setting COW and COLOR variables for MOTD (cf. Motd #22) and other ENV variables

[benknoble]

Should be writeable with a simple find one-liner after a check by [[ for the existence of the directory

[benknoble]

Requires that I move all my variable declarations and shopt/set/bind commands to the top of bashrc.

[benknoble]

Could do something along these lines (avoids find, requires .sh)

if [ -d /etc/profile.d ]; then
  for i in /etc/profile.d/*.sh; do
    if [ -r $i ]; then
      . $i
    fi
  done
  unset i
fi