Change the BSD license from 4 to 3-clause.

This makes it GPL compatible. Changing the license from 4 to 3-clause BSD
license is OK according to a Berkley announcement on July 22, 1999 by
William Hoskins, the director of the fofice of technology licensing for
Berkley:

ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change