jni: add GPLv2 header

close() is not called in the same thread than open()
DetachCurrentThread() worked though (did it do nothing?)

http://java.sun.com/docs/books/jni/html/refs.html

readMediaMeta: prepare for future extension of metadatas

don't use static variables when we can avoid
it might be true that we only have one Media instance in the program but we never know
also we must check for the condition because of spurious wakeups

check for the condition we're waiting for

merge .c & .h
use calloc to allocate sys_t
reorder functions to remove forward declaration
use static declarations