Improve diagnostic info in CommandT::Stub error message
Improve diagnostic info in CommandT::Stub error message

Was looking at this file while refactoring the MRU buffer code; took the
opportunity to leave it better. Hopefully this is the first of several
improvements that will make it easier to troubleshoot installation woes.

Signed-off-by: Wincent Colaiuta <c76ac2e9cd86441713c7dfae92c451f3e6d17fdc@wincent.com>

yrro/command-t,besarthoxhaj/command-t,vrkansagara/command-t,wincent/command-t,lencioni/command-t,wincent/command-t,1234-/command-t,supriyantomaftuh/command-t,lencioni/command-t,simichaels/dotfiles,vrkansagara/command-t,mtimkovich/command-t,mtimkovich/command-t,wincent/command-t,besarthoxhaj/command-t,yrro/command-t,supriyantomaftuh/command-t,1234-/command-t,simichaels/dotfiles