Grab some newer version of the autotools m4 archive, as we need those to setup code-coverage. Remove some unneeded ones.
Since we depend on autoconf-archive now, we don't need the copies of some of the m4 files, esp. since those break the autoconf-archive check in configure.ac.
Bump version to 0.9.19; add some extra warnings (using some new m4 macros)