Added more FTP tests. Refactored VFSFactory to VFSBuilder to be in line with the Test Builder pattern. Added a test to reproduce the double-barrel schema copy bug
Refactored the FtpSpec test case to derivce from abstract specification SchemaSpec
Fixed issue #8: Overwrite fails when using nested schemas (https://github.com/ysb33r/groovy-vfs/issues/8)