Add the prepare-commit-msg hook to the repository

[lwhsu]

Summary

This is a merged and modified version from src and ports repositories.

The easiest way to install is run the following command in the repository:

git config --add core.hooksPath .hooks

or copy it to the hooks directory, but it will not get automatically updated:

cp .hooks/prepare-commit-msg .git/hooks/

[carlavilla]

Approved, thanks for this