Revisit the name mangling rule usage for the '$' character (method and filenames named differently)

[pomadchin]

@jodersky also mentioned that it works here without extra rules for $.

This PR is made to check what's going on with the header functions generation.

Closes #36 (eventually)

Context

JDK8 javah preserves a specific file naming when dealing with generating methods for Scala objects. It generates filenames for objects that contain $ (all Scala objects) as package_ObjectName__.h (mangles $ into __). However, methods mangling is a bit different and for all methods it converts $ into _00024.

Right now in the master branch, for the following Adder.scala:

package multiclasses

object Adder {

  @native def sum(term1: Int, term2: Int): Int

}

The following multiclasses_Adder__.h would be generated:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class multiclasses_Adder__ */

#ifndef _Included_multiclasses_Adder__
#define _Included_multiclasses_Adder__
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:      multiclasses_Adder__
 * Method:     sum
 * Signature:  (II)I
 */
 // An incorrect method name is generated!
JNIEXPORT jint JNICALL Java_multiclasses_Adder___sum
  (JNIEnv *, jobject, jint, jint);

#ifdef __cplusplus
}
#endif
#endif

With this PR the following multiclasses_Adder__.h would be generated:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class multiclasses_Adder_00024 */

#ifndef _Included_multiclasses_Adder_00024
#define _Included_multiclasses_Adder_00024
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:      multiclasses_Adder_00024
 * Method:     sum
 * Signature:  (II)I
 */
JNIEXPORT jint JNICALL Java_multiclasses_Adder_00024_sum
  (JNIEnv *, jobject, jint, jint);

#ifdef __cplusplus
}
#endif
#endif

cc @jodersky do we need to preserve the original jdk8 javah filename?
The alternative can be just to remove a special case around $ and use the new namings generated by gjavah: multiclasses_Adder_00024.h which can be a bit more obvious (i.e. I would expect multiclasses_Adder_00024 methods to be stored in a multiclasses_Adder_00024.h file).

TLDR; the whole difference in behavior is in this diff: pomadchin@ea4ecc8

[pomadchin]

Closed in favor of #58 which I think makes more sense.