During work for JDK-8074387 for creation of golden files for negative tests, it was discovered that multiple error messages were generated when -source 6 was specified when compiling a test using JDK7 feature: strings in switch.

Test:tools/javac/StringsInSwitch/OneCaseSwitches.java

- compiler.warn.source.no.bootclasspath: 1.6
- compiler.warn.option.obsolete.source: 1.6
- compiler.warn.option.obsolete.suppression
OneCaseSwitches.java:23:15: compiler.err.string.switch.not.supported.in.source: 1.6
OneCaseSwitches.java:33:15: compiler.err.string.switch.not.supported.in.source: 1.6
OneCaseSwitches.java:52:15: compiler.err.string.switch.not.supported.in.source: 1.6
OneCaseSwitches.java:66:15: compiler.err.string.switch.not.supported.in.source: 1.6
OneCaseSwitches.java:85:15: compiler.err.string.switch.not.supported.in.source: 1.6
OneCaseSwitches.java:99:15: compiler.err.string.switch.not.supported.in.source: 1.6
OneCaseSwitches.java:119:15: compiler.err.string.switch.not.supported.in.source: 1.6
OneCaseSwitches.java:130:15: compiler.err.string.switch.not.supported.in.source: 1.6
neCaseSwitches.java:242:16: compiler.err.string.switch.not.supported.in.source: 1.6
9 errors
3 warnings