Makefile enhancements: (1) Rename autoconf/tea/configure.in to

autoconf/tea/configure.ac so that it works with the latest versions of
autoconf.  (2) Add the "amalgamation-tarball" targets to Makefile.in and
main.mk (renamed from "dist" in the latter case).  (3) Update the
README.first file in autoconf/  (4) The TOP macro
in Makefile.in is now an absolute rather than a relative path.

FossilOrigin-Name: 3bafeec934e56f633d0de6890e84fca990e54435