Add copyright notice to the top of each file.

Makefile:
Mercury.options:
basic.m:
mfcgi.m:
mfcgi_test.m:
mfcgi_threadtest.m:
multi.m:
streams.m:
    As above.

LICENSE:
    Removed "All rights reserved".
Mark some thread safe predicates as thread safe.

basic.m:
streams.m:
    As above.
Minor fixes

streams.m:
mfcgi.m:
multi.m:
    Make corrections to some comments.

basic.m:
    Fix a variable name.

basic.m:
multi.m:
    Fix whitespace.