[m-rev.] for review: bump the minimum version of Java required

[Julien Fischer]

I forgot to update the configure test in my last diff, revised one
follows:

--------------------------

Bump the minimum version of Java required.

NEWS:
README.Java:
     Required at least Java SE 6 or equivalent.

m4/mercury.m4:
     Check for at least the above version of Java.

Julien.

diff --git a/NEWS b/NEWS
index 1deb127..4b61dbd 100644
--- a/NEWS
+++ b/NEWS
@@ -88,6 +88,9 @@ Changes that may break compatibility:
  * We have deleted the builtin modes `no' and `oo': their uses should be
    replaced with `oa' and `ia' respectively.

+* The minimum version of the Java platform required by Mercury's Java
+  backend is now Java SE 6.
+
  Changes to the Mercury language:

  * We have added a new kind of scope to the language: determinism checks
diff --git a/README.Java b/README.Java
index b222ec7..c129c12 100644
--- a/README.Java
+++ b/README.Java
@@ -2,24 +2,22 @@

  INTRODUCTION

-This release of Mercury contains a port to Java,
-in particular to Sun Microsystems' Java 2 Platform, Standard Edition (J2SE).
-The Mercury compiler will generate Java source code that can be compiled into
-Java bytecode suitable for running in the J2SE runtime system.
+The Mercury compiler can generate Java source code that can be compiled into
+Java bytecode suitable for running the Java SE runtime system.  The port is
+mostly complete, but some parts of the Mercury standard library are not yet
+implemented (for a full list see the FAQ below).

-The port is mostly complete, but some parts of the Mercury standard
-library are not yet implemented (for a full list see the FAQ below).
-
-The port is currently targeted at J2SE version 1.5 or higher.
+The port requires Java SE 6 or higher -- older versions of Java are *not*
+supported.

  PREREQUISITES

  In order to try this system you will need

-	- The J2SE SDK, which can be downloaded for free from
-		<http://java.sun.com/downloads/index.html>
+    * The J2SE SDK, which can be downloaded for free from
+      <http://www.oracle.com/technetwork/indexes/downloads/index.html>

-	  OR any other compatible Java implementation.
+    * OR any other compatible Java implementation, such as OpenJDK.

  -----------------------------------------------------------------------------

diff --git a/m4/mercury.m4 b/m4/mercury.m4
index c93623c..a81f645 100644
--- a/m4/mercury.m4
+++ b/m4/mercury.m4
@@ -492,7 +492,7 @@ if test "$JAVAC" != "" -a "$JAVA_INTERPRETER" != "" -a "$JAR" != ""; then
  	cat > conftest.java << EOF
  		// This program simply retrieves the constant
  		// specifying the version number of the Java SDK and
-		// checks it is at least 1.5, printing "Hello, world"
+		// checks it is at least 1.6, printing "Hello, world"
  		// if successful.
  		public class conftest {
  		    public static void main (String[[]] args) {
@@ -512,7 +512,7 @@ if test "$JAVAC" != "" -a "$JAVA_INTERPRETER" != "" -a "$JAR" != ""; then
  				version = 0f;
  			}

-			if (version >= 1.5f) {
+			if (version >= 1.6) {
  				System.out.println("Hello, world\n");
  			} else {
  				System.out.println("Nope, sorry.\n");