eepget: If java binary is not found, try to determine where java.exe is located.

In my testing:
32 bit Windows (and, of course, 32 bit JRE) = Java added to the PATH
64 bit Windows and 64 bit JRE = Java added to the PATH
64 bit Windows and 32 bit JRE = Java *not* added to the PATH.

So...with this check-in:

- If the environment variable JAVA is set in the script, we'll use that
  manually specified Java. We will not look in the registry, but we'll check to
  make sure that the binary exists.
- If Java is found in the system path, we'll use it instead. We will not look in the
  registry.
- If the variable is not set manually and Java is not in the system path we'll
  look in the registry to find the java binary.

I've tested this in Windows XP, Vista, and 7 but it should work in any supported version
of Windows.