get address of jvm functions on both osx and linux

On osx libjvm.so is called libjvm.dylib, not libjvm.so. To fix loading of jvm functions on both linux and osx, I skip the reference to libjvm and use dlsym(RTLD_DEFAULT). This is a fix for the issue #52 I reported.

linux manpage dlsym(3):

"There are two special pseudo-handles, RTLD_DEFAULT and RTLD_NEXT. The former will find the first occurrence of the desired symbol using the default library search order. "

osx manpage dlsym(3):

"If dlsym() is called with the special handle RTLD_DEFAULT, then all mach-o images in the process (except those loaded with dlopen(xxx, RTLD_LOCAL)) are searched in the order they were loaded.  This can be a costly search and should be avoided."

Tested on OSX 10.9 and Ubuntu 12.04 both with java 8u11