added mailmap with entry for Adam Ralph

It seems something weird happened with the email addresses for the commits in the history. This can be fixed by adding a .mailmap file with appropriate mappings. I've added an entry for myself and I guess other authors can later add mappings for themselves or for others who they are familiar with.

Before:
![image](https://f.cloud.github.com/assets/677704/2323516/b6889724-a3bd-11e3-9f18-40096b6401c6.png)
After:
![image](https://f.cloud.github.com/assets/677704/2323521/c733d444-a3bd-11e3-88e0-608f3759fdcc.png)