Spurious notification that the test plan has changed

**Sebb** ([Bug 56159](https://bz.apache.org/bugzilla//show_bug.cgi?id=56159&redirect=false)):
It looks as though the addition of the jmeter version attribute to the jmeterTestPlan tag in the JMX file has the unfortunate side effect of marking the plan "dirty" and asking whether to save it on exit.

Ideally we need to suppress the warning if the only change is the jmeter version.
In fact the other attributes on the jmeterTestPlan should probably not cause the plan to be marked dirty either.

Severity: normal
OS: Windows XP