Handle local imports correctly.
Handle local imports correctly.

Various fixes here to enable coverage testing of
code.google.com/p/goprotobuf/proto.
- Only instrument test files from the initial package.
- Bail out early if there are no test files.
- Resolve local imports to absolute package paths.

Fixes Issue #9.

cmars/gocov,cmars/tools,cmars/tools,cmars/tools,cmars/tools