Improve glgen

+ gen script is really a bash script rather than a sh script,
  so declare that to be true. (For example, it uses pushd,
  which is a part of bash, but not a part of sh. Not sure
  how this worked until now. Possibly gen was only run in
  environments where /bin/sh was really bash.

+ Check the results of the java compile of the code generator,
  and abort the script if the compile fails.

+ Turn on the bash shell option that guards against using
  uninitialized variables in the script.

+ Remove the generated class files.

Refactor JniCodeEmitter into two classes: a general-purpose
JniCodeEmitter and a specific Jsr239CodeEmitter. The hope is
to use JniCodeEmitter as a base for emitting static OpenGL ES
bindings.
diff --git a/opengl/tools/glgen/src/Jsr239CodeEmitter.java b/opengl/tools/glgen/src/Jsr239CodeEmitter.java
new file mode 100644
index 0000000..eff0447
--- /dev/null
+++ b/opengl/tools/glgen/src/Jsr239CodeEmitter.java
@@ -0,0 +1,74 @@
+import java.io.PrintStream;
+
+/**
+ * Emits a Java interface and Java & C implementation for a C function.
+ *
+ * <p> The Java interface will have Buffer and array variants for functions that
+ * have a typed pointer argument.  The array variant will convert a single "<type> *data"
+ * argument to a pair of arguments "<type>[] data, int offset".
+ */
+public class Jsr239CodeEmitter extends JniCodeEmitter implements CodeEmitter {
+
+    PrintStream mJava10InterfaceStream;
+    PrintStream mJava10ExtInterfaceStream;
+    PrintStream mJava11InterfaceStream;
+    PrintStream mJava11ExtInterfaceStream;
+    PrintStream mJava11ExtPackInterfaceStream;
+    PrintStream mJavaImplStream;
+    PrintStream mCStream;
+
+    PrintStream mJavaInterfaceStream;
+
+    /**
+     * @param java10InterfaceStream the PrintStream to which to emit the Java interface for GL 1.0 functions
+     * @param java10ExtInterfaceStream the PrintStream to which to emit the Java interface for GL 1.0 extension functions
+     * @param java11InterfaceStream the PrintStream to which to emit the Java interface for GL 1.1 functions
+     * @param java11ExtInterfaceStream the PrintStream to which to emit the Java interface for GL 1.1 Extension functions
+     * @param java11ExtPackInterfaceStream the PrintStream to which to emit the Java interface for GL 1.1 Extension Pack functions
+     * @param javaImplStream the PrintStream to which to emit the Java implementation
+     * @param cStream the PrintStream to which to emit the C implementation
+     */
+    public Jsr239CodeEmitter(String classPathName,
+                          ParameterChecker checker,
+                          PrintStream java10InterfaceStream,
+                          PrintStream java10ExtInterfaceStream,
+                          PrintStream java11InterfaceStream,
+                          PrintStream java11ExtInterfaceStream,
+                          PrintStream java11ExtPackInterfaceStream,
+                          PrintStream javaImplStream,
+                          PrintStream cStream,
+                          boolean useContextPointer) {
+        mClassPathName = classPathName;
+        mChecker = checker;
+        mJava10InterfaceStream = java10InterfaceStream;
+        mJava10ExtInterfaceStream = java10ExtInterfaceStream;
+        mJava11InterfaceStream = java11InterfaceStream;
+        mJava11ExtInterfaceStream = java11ExtInterfaceStream;
+        mJava11ExtPackInterfaceStream = java11ExtPackInterfaceStream;
+        mJavaImplStream = javaImplStream;
+        mCStream = cStream;
+        mUseContextPointer = useContextPointer;
+    }
+
+    public void setVersion(int version, boolean ext, boolean pack) {
+        if (version == 0) {
+            mJavaInterfaceStream = ext ? mJava10ExtInterfaceStream :
+                mJava10InterfaceStream;
+        } else if (version == 1) {
+            mJavaInterfaceStream = ext ?
+                (pack ? mJava11ExtPackInterfaceStream :
+                 mJava11ExtInterfaceStream) :
+                mJava11InterfaceStream;
+        } else {
+            throw new RuntimeException("Bad version: " + version);
+        }
+    }
+
+    public void emitCode(CFunc cfunc, String original) {
+        emitCode(cfunc, original, mJavaInterfaceStream, mJavaImplStream, mCStream);
+    }
+
+    public void emitNativeRegistration() {
+        emitNativeRegistration(mCStream);
+    }
+}