The survey package has benefited from code, bug reports, and feature 
requests from users, including:
  Daniel Almirall
  Stefano Calza
  Daniella Gollinelli
  Ana Patricia Martins
  Daryl Morris
  Ana Quiterio
  Gillian Raab
  Fred Rohde
  Steve Roberts
  Andrew Robinson
  Lee Sieswerda
  Takahiro Tsuchiya
  Tobias Verbeke
  Renzo Vettori
  Alan Zaslavksy
and from initial dicussions with Chris Wild and Alastair Scott. 

There are probably others who should be listed but whose names have been
lost due to poor record-keeping. 

