Giving permission to use the Boost Software License for my Boost code

[SVN r21136]

more/blanket-permission.txt

@@ -5,3 +5,4 @@ License, Version 1.0.
 David Abrahams (dave@boost-consulting.com)
 Beman Dawes (bdawes@acm.org)
 Daniel Frey (d.frey -at- gmx.de, daniel.frey -at- aixigo.de)
+Douglas Gregor (greod@cs.rpi.edu)