Add autoconf CIG m4 macros
Added m4 submodule
Added archimedes python module manually.

In the SVN repository archimedes was an external repository. Since it is just a single file and hasn't changed in several years and it is likely to go away, the file was added manually rather than using a submodule.
Added .gitignore.

Developers will want to add patterns like *.pyc to their global ignore rules.
Added other autoconf repo references
Updated submodules
Fixed use of const in return values to resolve warnings from Intel compiler.
Merge branch 'next' of github.com:geodynamics/pylith into next