Made display_text_file() to get the scroll speed as an argument. This way we can...

Made display_text_file() to get the scroll speed as an argument. This way we can make the intro slower than the credits, for instance. It was just impossible to read them.
Anyway, you can easily change their speed in defines.h .

Also fixes a bug that was making the text to take while before starting to be displayed.

SVN-Revision: 811