Fix file creation

Ensure checkPath passes the actual file path to its callback, so that files are created in the right directory instead of the torrent basePath.
Merge pull request #16 from njoyard/patch-1

Fix file creation
Prevent invalid peer connections

Ignore peer connections with ports outside 1-65535 (which make dht.js throw exceptions)
Prevent torrents from changing client._extensions

Without this change, adding several torrents to the same client causes exceptions because torrents change client._extensions (torrent.js:209)
Merge pull request #18 from njoyard/patch-1

Prevent invalid peer connections
Merge pull request #19 from njoyard/patch-2

Prevent torrents from changing client._extensions
Merged upstream changes