FileDescriptor.java: Implement on top of FileChannel.

	* java/io/FileDescriptor.java:  Implement on top of FileChannel.
	Remove native methods.

	* java/io/natFileDescriptorEcos.cc:  Remove file.
	* java/io/natFileDescriptorPosix.cc:  Remove file.
	* java/io/natFileDescriptorWin32.cc:  Remove file.
	* java/io/FileInputStream.java (ch):  Change type to FileChannelImpl.
	(<init>(File)):  Allocate a FileChannelImpl, not a FileDescriptor.
	(<init>(FileChannelImpl)):  New package-private constructor.
	(<init>(FileDescriptor)):  Extract FileChannelImpl from arg.
	(available, close, read, skip):  Implement using FileChannelImpl.
	(getFD):  Allocate FileDescriptor if needed.
	(getChannel):  Is now trivial.
	* java/io/FileOutputStream.java:  Corresponding changes.
	* java/io/RandomAccessFile.java:  Corresponding changes.

From-SVN: r78661