split out logical for getting available ponies

Signed-off-by: Mattias Andrée <maandree@operamail.com>
split out the pony restriction logic

Signed-off-by: Mattias Andrée <maandree@operamail.com>
split out the logic for randomly selecting a pony when none is selected

Signed-off-by: Mattias Andrée <maandree@operamail.com>
m fix

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Merge branch 'master' of github.com:erkin/ponysay