Goodbye jigsaw/stage forest, hello jigsaw/m2 forest

[Alan Bateman]

Now that the source code layout and the changes to build by module are 
in JDK 9 it means that the temporary staging forest (jigsaw/stage) that 
we used to prepare those changes should no longer be needed. To that 
end, jigsaw/stage has been renamed to jigsaw/m1 and changed to be read-only.

Next up is modularizing the structure of the binary images (what we know 
today as the JDK and JRE builds in $OUTPUT_DIR/images). There will be a 
JEP with a detailed proposal on this soon. We expect there will 
significant infrastructure work in this milestone and we need a forest 
to collect the various prototype and other pieces that will be needed. 
To that end, we have a new forest jigsaw/m2 [1] that we will be using 
for this work. It is initially cloned from jdk9-b28.

-Alan.

[1] http://hg.openjdk.java.net/jigsaw/m2