Added message which displays the estimate travel time

One of my friends suggested this feature and I really liked the idea, so I decided to add it myself quickly and submit a Pull Request for it!

This Pull Request adds an extra message line whenever a player starts a travel on the same world - it will calculate a rough estimate of how long the flight will take based on the distance between the two locations and the travel speed.

![screenshot 2014-01-10 16 00 40](https://f.cloud.github.com/assets/551935/1888084/346332e2-7a08-11e3-8dc4-4796bb2c7746.png)