Clarify licensing in READMEs.

Say that the GPL terms apply to the compiler and tools, not to the
"implementation".  As stated right after, the libraries and runtime are
distributed under the terms of the LGPL.

Don't say Mercury is free software "but" it is copyrighted.
There's nothing strange about it.

Fix spelling ("licence" is a noun).

.README.in:
bindist/bindist.README:
	As above.
Update NEWS file for 13.05 release.

NEWS:
	Merge the NEWS for 12.08 (which we won't officially
	release) with other recent changes to form the NEWS
	file for the 13.05 release.
Update bootcheck script for mfilterjavac.

tools/bootcheck:
    As above.
Install mfilterjavac from the top-level install target.

Mmakefile:
	As above.
Disable mfilterjavac for now.

mfilterjavac is currently causing problems when installing the java grade from
the stage 2 dir.  It can be re-enabled when the following sequence of actions
works correctly:

(1) Build stage 1 using rotd-2013-04-18
(2) Bootcheck (or otherwise build the stage 2 compiler).
(3) cd stage2 && mmake install (with the java grade as one of the grades
    to install).

compiler/options.m:
	Disable the use of mfilterjavac for now.

compiler/mlds_to_java.m:
	Update a comment.
Update the tar and touch_files targets for mfilterjavac.

Mmakefile:
	As above.