Build with java7 by default.

All introduce a flag LEGACY_USE_JAVA6 to force java6 builds.
This is an unsupported configuration, and provided temporarily
to iron out regressions and compare build output (if required.).

- Increment the version check sequence number.
- Move a more specific check (OpenJDK vs non OpenJDK) after
  the more general version check.
- Update the link in the version check error message to the
  "initializing" page instead of the "download" page. The latter
  talks about repo, mainly.

bug: 8992787

Change-Id: I313e17b1911768d4f3bc318c4162c53dec6eaf0d

Conflicts:
	core/main.mk

envsetup.sh

@@ -1380,7 +1380,8 @@ function godir () {
 # JavaVM.framework/Versions/1.7/ folder.
 function set_java_home() {
     # Clear the existing JAVA_HOME value if we set it ourselves, so that
-    # we can reset it later, depending on the value of EXPERIMENTAL_USE_JAVA7.
+    # we can reset it later, depending on the version of java the build
+    # system needs.
     #
     # If we don't do this, the JAVA_HOME value set by the first call to
     # build/envsetup.sh will persist forever.
@@ -1389,7 +1390,7 @@ function set_java_home() {
     fi
 
     if [ ! "$JAVA_HOME" ]; then
-      if [ ! "$EXPERIMENTAL_USE_JAVA7" ]; then
+      if [ -n "$LEGACY_USE_JAVA6" ]; then
         case `uname -s` in
             Darwin)
                 export JAVA_HOME=/System/Library/Frameworks/JavaVM.framework/Versions/1.6/Home