Eclipse Helper: stop early when we know it's not Eclipse

Eclipse would never add the current directory to the class path;
therefore, when we detect that the current directory was added as
'.', we can just as well stop annotating indexes right away.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #19 from scijava/annotation-indexer

Eclipse Helper: stop early when we know it's not Eclipse