fix OS version detection on Windows

On Windows, the consumer-known version is included in the os.name
property, with Microsoft's internal version number in os.version.
The internal version number isn't very useful, and is also kind of
weird (for example, Windows 7's os.version is 6.1). So, it now checks
for "Windows " in os.name, and doesn't print os.version in that
case.

jes/java/JESVersion.java.in

@@ -39,21 +39,36 @@ public class JESVersion {
         return SCM_INFO;
     }
 
+    public static String getOSVersion () {
+        String name = System.getProperty("os.name");
+
+        // Windows includes the version the user would know in os.name.
+        // The os.version property doesn't include anything useful.
+        // (For example, os.name is "Windows 7" and os.version is "6.1"
+        // on my Windows 7 laptop.)
+        // So, on Windows platforms, we only return the name.
+        // It is more useful on OS X and Linux.
+        if (name.startsWith("Windows ")) {
+            return name;
+        } else {
+            return name + " " + System.getProperty("os.version");
+        }
+    }
+
     public static String getMessage () {
         return String.format(
             "JES version %s\n" +
             "Release date:   %s\n" +
             "Source control: %s\n" +
             "Java version:   %s (%s/%s)\n" +
             "Jython version: %s (build %s)\n" +
-            "Computer OS:    %s %s (%s architecture)",
+            "Computer OS:    %s (%s architecture)",
             RELEASE, RELEASE_DATE, SCM_INFO,
             System.getProperty("java.version"),
             System.getProperty("java.runtime.name"),
             System.getProperty("java.vm.name"),
             org.python.Version.PY_VERSION, org.python.Version.getBuildInfo(),
-            System.getProperty("os.name"), System.getProperty("os.version"),
-            System.getProperty("os.arch")
+            getOSVersion(), System.getProperty("os.arch")
         );
     }
 }