Add declaration of boost project.

[SVN r19988]

Jamrules

@@ -1,6 +1,7 @@
 # Boost.Build top level Jamrules
 
 # See tools/build/index.html for documentation.
+project boost ;
 
 # Set some important global variables if they haven't already been set by the
 # user on the command-line or in the environment