Add optional message parameter to requireAdmin()
Add optional message parameter to requireAdmin()

This adds an optional message parameter to requireAdmin(). When provided, the
message replaces the default 'Administrator access required' message, presumably
with something more descriptive.

girder/girder,adsorensen/girder,adsorensen/girder,essamjoubori/girder,jbeezley/girder,salamb/girder,girder/girder,Kitware/girder,kotfic/girder,salamb/girder,essamjoubori/girder,adsorensen/girder,data-exp-lab/girder,sutartmelson/girder,RafaelPalomar/girder,Kitware/girder,Kitware/girder,RafaelPalomar/girder,data-exp-lab/girder,RafaelPalomar/girder,jbeezley/girder,essamjoubori/girder,adsorensen/girder,jbeezley/girder,kotfic/girder,Xarthisius/girder,manthey/girder,kotfic/girder,salamb/girder,RafaelPalomar/girder,sutartmelson/girder,data-exp-lab/girder,essamjoubori/girder,sutartmelson/girder,girder/girder,girder/girder,Xarthisius/girder,jbeezley/girder,Xarthisius/girder,salamb/girder,data-exp-lab/girder,sutartmelson/girder,manthey/girder,kotfic/girder,manthey/girder,manthey/girder,salamb/girder,Xarthisius/girder,adsorensen/girder,data-exp-lab/girder,essamjoubori/girder,RafaelPalomar/girder,Xarthisius/girder,kotfic/girder,sutartmelson/girder,Kitware/girder