Respect the JAVA_HOME environment variable

When the JAVA_HOME environment variable is set, use it to find the java
executable for launching java subprocesses.
Update ReleaseNotes for JAVA_HOME change
Fix unit tests broken by 93961744c
Merge pull request #422 from jonrward/respect-JAVA_HOME

Respect the JAVA_HOME environment variable

Conflicts:
	FitNesseRoot/FitNesse/ReleaseNotes/content.txt