Implement NTRU_AVOID_HAMMING_WT_PATENT; make Makefiles more consistent

The NTRU_AVOID_HAMMING_WT_PATENT preprocessor flag removes all code affected by U.S. patent 7031468.
This commit also applies commits 1308bb40 and 67a2fbff to Makefile.win and Makefile.osx for consistency.
Remove patent 6298137 as it doesn't seem to affect libntru; change wording