port GsDevKit-Structure packages to GemStone 3.5.0

[dalehenrich]

Part of Issue #260. The GsDevKit-Structure package provides support for navigating the GsDevKit_home directory structure. The functionality in the GsDevKit-CommandLine package depends upon the GsDevKit-Structure package.

• [ ] get GsDevKit-Structure package to load into GemStone 3.5.0
• [ ] get GsDevKit-Tests-Structure tests to pass