package.json is now generated by configure script and included in distribution
Added necessary EXTRA_DIST files for successful dist build
Corrected @setfilename for easejs.texi
AUTHORS, NEWS, and ChangeLog may now be built independently
Corrected doc Makefile EXTRA_DIST img/
AUTHORS, NEWS, ChangeLog, and package.json can now be cleaned
signchk tool now only checks merge commit (not the commits introduced) for signature

This greatly simplfies rebasing and other operations while working in a branch;
signing each and every commit that is not in master can be overkill (even if it
does give peace of mind).