#1617: Add :browse! and various other additions to GHCi

   
  - :browse!
    a variant of :browse that lists children separately,
    not in context, and gives import qualifiers in comments

SimonM: I also added sorting by source location for interpreted
modules in :browse, and alphabetic sorting by name otherwise.  For
:browse *M, the locally-defined names come before the external ones.

  - :{ ..lines.. :} (multiline commands)
    allow existing commands to be spread over multiple lines
    to improve readability, both interactively and in .ghci
    (includes a refactoring that unifies the previous three
    command loops into one, runCommands, fed from cmdqueue,
    file, or readline)

  - :set
      now shows GHCi-specific flag settings (printing/
      debugger), as well as non-language dynamic flag 
      settings
    :show languages
      show active language flags
    :show packages
      show active package flags as well as implicitly 
      loaded packages