Work around test failures in 2.11.0-M8, due to SI-8205

The compiler fix is in https://github.com/scala/scala/pull/3427

In the meantime, to have at least one Scala-search commit that builds on
the 2.11.0-M8 release, this reinstates the old SourceFile.lineToString.
Merge pull request #84 from huitseeker/issue/SI-8205

Work around test failures in 2.11.0-M8, due to SI-8205