PlatformPropsImpl: JAVA_RUNTIME_NAME is null using GCJ gij JRE.

Signed-off-by: Xerxes Rånby <xerxes@zafena.se>
Buffer.isDirect() operation is undefined w/ Eclipse ecj and GCJ gij JRE.

Fix for the runtime error using GCJ gij JRE:
java.lang.NoSuchMethodError: method java.nio.Buffer.isDirect with signature ()Z was not found.
at com.jogamp.common.nio.Buffers.isDirect(Buffers.java:363)

Also Eclipse ecj refuses to compile code using java.nio.Buffer.isDirect().
----------
1. ERROR
...
        return ((Buffer) buf).isDirect();
	                      ^^^^^^^^
The method isDirect() is undefined for the type Buffer

Signed-off-by: Xerxes Rånby <xerxes@zafena.se>
Merge remote-tracking branch 'xranby/gcj-gij'
Modified Java 1.5 Buffers patch 2b7d1b1d25cb2cd73311ec9159b465f0391bf5e0 - May break GCJ/ECJ .. needs to be revised.

- Adding JAVA_6 in PlatformPropsImpl
- Buffers.isDirect() chooses fast-path iff JAVA_6, otherwise using reflection (GCJ/ECJ)
- Adding JAVA_6 info in VersionUtil
- API doc: Refine JAVA_SE and JAVA_6 spec.

TODO: In case GCJ etc is unable to compile the JAVA_6 code
      even though it uses a static condition (probably not),
      We have to wrap isStatic in an own class, one for JAVA_6 and one for <= 1.5.
      This will be a good exercise for further issues we may have w/ Java <= 1.5.