Display Java stacktrace by default in JavaException (#696)

* WIP - java exception printing

* try str instead

* change reporting of Java exception name to be more java-like

* use args[0] for the message

* address spacing

jnius/jnius_export_class.pxi

@@ -14,6 +14,15 @@ class JavaException(Exception):
         self.stacktrace = stacktrace
         Exception.__init__(self, message)
 
+    def __str__(self):
+        '''
+        Override __str__ so that we can see the Java stacktrace
+        '''
+        rtr = self.args[0]
+        if self.stacktrace is not None:
+            rtr += '\n' + '\n\t'.join(self.stacktrace)
+        return rtr
+
 
 cdef class JavaObject(object):
     '''Can contain any Java object. Used to store instance, or whatever.

jnius/jnius_utils.pxi

@@ -76,7 +76,7 @@ cdef void check_exception(JNIEnv *j_env) except *:
             j_env[0].DeleteLocalRef(j_env, e_msg)
         j_env[0].DeleteLocalRef(j_env, exc)
 
-        raise JavaException('JVM exception occurred: %s' % (pymsg + " " + str(pyexcclass) if pymsg is not None else pyexcclass), pyexcclass, pymsg, pystack)
+        raise JavaException('JVM exception occurred: %s' % (str(pyexcclass) + ": " + pymsg if pymsg is not None else pyexcclass), pyexcclass, pymsg, pystack)
 
 
 cdef void _append_exception_trace_messages(