FileChannelImpl.java: New class, renamed from java/nio/channels.

	* gnu/java/nio/channels/FileChannelImpl.java:  New class, renamed
	from java/nio/channels.  Don't depend on FileDescriptor.
	(in, out, err):  New static fields.
	(mode):  New field.
	(SET, CUR, READ, WRITE, APPEND, EXCL, SYNC, DSYNC):  Moved constants
	from FileDescriptor.
	(by):  Removed MappedByteBuffer field.
	(map):  New working implementation.
	* gnu/java/nio/channels/natFileChannelPosix.cc:  New file, though
	some code "ported" from natFileDescriptoPosix.cc.
	* gnu/java/nio/channels/natFileChannelEcos.cc:  Likewise.
	* gnu/java/nio/channels/natFileChannelWin32.cc  Likewise.

From-SVN: r78659