- only read ~/.ghci if it is owned by the current user and isn't
  writable by anyone else.

- Only read ./.ghci if both . and ./.ghci are owned by the current
  user and aren't writable by anyone else.  I think this is
  sufficient: we don't need to check .. and ../.. etc. because "."
  always refers to the same directory while a process is running.

- Don't load .so libraries in a package if that package is already
  linked with GHCi.  This stops us re-linking libm, libreadline etc.

- Allow packages to be loaded from within GHCi using
	:set -package <name>
  NOTE: this will unload all modules currently loaded into the
  interpreter.  I did this to be on the safe side - I think perhaps
  it isn't necessary, but I haven't thought it through fully yet.

- fix CompManager.cmUnload in the process.  It was wrong in several
  ways.

MERGE WITH 5.00