Replace references to CVS with git

[fangism]

Current versions of git don't honor .cvsignore files anymore.
This project started in CVS in 2004 before it was migrated to git in 2010.
There never existed a public CVS repo, so there is zero reason to retain any references to CVS.
It's time to migrate.

Files to migrate include:

• configure, Make-related files
• .cvsignore files and snippets
• maintainer documentation

[fangism]

At the same time, it might also be a good idea to move to static .gitignore files, rather than generating pieces of them.
git's ignore-semantics are richer than cvs's.