Fix links on page about .NET back-end.
Try to clarify licensing.

The main download page simplified the licensing terms.  The separate
'license' page stated the full situation but included a full copy of
only the GPL which may be misleading.  Including both the GPL
and LGPL would be too much.

include/download.inc:
	Move the licensing statement to the top of the main download
	page.

	Link to the (text) copies of the GPL and LGPL instead of
	reproducing them inline.

download/COPYING:
download/COPYING.LIB:
	Add these files from the Mercury distribution.

download/license.php:
include/menubar.inc:
	Delete separate license page.
Replace quote on the main page.

The old text was a placeholder and would be misleading regarding
the licensing.  The new text is a slightly condensed version of
the opening line from the JICSLP '96 Workshop slides.

include/index.inc:
	As above.