Makefile.am update

Update Makefile.am in a few ways.  Avoid tabs inside variables which
messes up cut-and-paste of generated shell commands in terminal
windows.  Avoid gratuitous use of scrypt_.  Include all the files
in the "make dist" tarball, include *.h by adding them to _SOURCES,
which is the approved way per the automake info pages.  Avoid stepping
on CFLAGS which is reserved for the user, instead use AM_...
configure.ac standardize

Add standard constructs and comments and do things in standard ways
and in the standard order.