bugfix/7175-openjdk-7 workarounds #7175 (aka. "Sikuli is broken with
openjdk 6b31-1.13.3-1~deb7u1") by using OpenJDK 7 (instead of 6) to
run our test suite. Please review'n'merge. Assigned to anonym, who'll
need this fix to run the 1.1 automated test suite.