improve require version messages for shiny and httpuv
add module context function to detect osx mavericks
prevent osx mavericks svn and git install dialog from popping up
viewer: use absolute session temp dir url in desktop mode
viewer: eliminate print command and use iframe src property for refresh

both of these changes were to eliminate cross-domain errors in desktop mode (where the viewer is running on a different port)
restore busy state when executing commands from a browser prompt
Merge remote-tracking branch: upstream/master