Bug Fixes for Inconsistent Download Location with FlexGet

The commits in this pull request resolve both bugs which cause [Inconsistent Download Locations with FlexGet](https://github.com/pyload/pyload/issues/808) (issue #808).

The modification of pyPackage resolves the first bug, which causes download locations passed by FlexGet to be mangled from (for example) X:\Intended\Folder to D:\Default pyLoad Download Folder\XIntendedFolder.

The modifications of the API and FlexGet's pyload output plugin resolve the second bug, which causes download locations passed by FlexGet to be mangled from (for example) X:\Intended\Folder to D:\Default pyLoad Download Folder\Package Name. The modifications of the API are such that they maintain compatibility with FlexGet for installations which have not been updated to the new pyload output plugin, although the fix won't work until it is.