The command line script fails with a cryptic error if the java executable cannot be found

[Leif Singer]

If the java executable cannot be found -- i.e., probably JAVA_HOME isn't set right -- the ´play´ command fails with a traceback similar to this, giving no direct clue as to what the reason for failure is:

Traceback (most recent call last):
  File "/Applications/play/play", line 805, in <module>
    pid = subprocess.Popen(java_cmd, stdout=sout, env=os.environ).pid
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 595, in __init__
    errread, errwrite)
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 1106, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

This should be replaced with a more meaningful error message.