Use $target_file in *_get variables, not $name

When a user specifies the $target parameter in a staging::file defined
type, the intention is to fetch the file from $source and place it at
$target. When $name is used in the $http_get variants, the retrieved
file won't actually be placed at the $target location. This commit makes
it so that curl and wget will always place the retrieved file in the
$target_file location. This should not impact the behavior when a user
doesn't specify $target, but should fix the unexpected behavior when
they do.
Update spec tests to reflect absolute target

Now that $target_file is being used to specify the download location for
curl commands, the command expected in the tests has changed. This
commit updates the tests to reflect that change.
fix typo in error message
Merge pull request #27 from justinclayton/patch-2

fix typo in error message
Merge pull request #24 from reidmv/fix_target_path

Use $target_file in *_get variables, not $name