RFR: JDK-8087329: Introduce VERSION_IS_GA

[Erik Joelsson]

Hello,

Please review this change to the new build number implementation in 
project Verona. This change is intended to go into the Verona forest for 
now until it's time for integration into jdk9.

By definition, the way to determine from the version string if a release 
is a GA release or a pre-release is to check if the PRE string is empty. 
If it is empty, it's a GA release, otherwise it's not. While this is 
logical from a theoretical point of view, it is not immediately obvious 
to developers. One place in the OpenJDK where such a check is done is 
make/Javadoc.gmk.

In this patch, a new make variable is introduced: VERSION_IS_GA, which 
can be either true or false.

Bug: https://bugs.openjdk.java.net/browse/JDK-8087329
Webrev: http://cr.openjdk.java.net/~erikj/8087329/webrev.01/

/Erik