Pushes the output of InterruptedExceptions to debug log level

This is a companion to https://github.com/scala-ide/scala-ide/pull/481 in the sense that testing this PR revealed InterruptedExceptions being treated and passed in the askOption exception capture mechanism, in very long documentation requests.
This logs such exceptions at debug level, and hints at issue in comments.
Merge pull request #541 from huitseeker/suppress-interrupted-exception

Pushes the output of InterruptedExceptions to debug log level