Creates the fixturs folder if needed

With this change, if the fixtures folder does not exists
the propel:fixtures:dump command asks user's confirmation
for its creation. If the user deny the authorization, the command
will throw a IOException (before file_put_contents rises a warning).
Merge pull request #225 from lucasaba/unclear-exception-on-propel-fixtures-dump

Creates the fixtures folder if needed
Merge branch '1.2' into survos