fixed bug in dependency validation

error messages should be a lot more helpful now
Add compression (scp -C) for RemoteTarget get/put
make luigid state file path configurable

Use `state-path` option of the [scheduler] section to adjust
the state path file location.

Addresses [#188](https://github.com/spotify/luigi/issues/188).
Added missing import to interface.py
Issue #199 - move reducer initializing to base class

Change-Id: I54bc142b4f17789a7bc4c06e50b4a87b12149091
Merge pull request #200 from edwardnewett/master

Issue #199 - move reducer initializing to base class
Merge pull request #186 from erikbern/validate-dep-error

fixed bug in depdency validation
Merge pull request #191 from sisidra/master

Add compression (scp -C) for RemoteTarget get/put
Merge pull request #195 from miku/issue-188

make luigid state file path configurable
Merge pull request #196 from davidxia/master

Added missing import to interface.py