Normally version control systems don't allow fine grained commits. 
commit-patch allows the user to control exactly what gets committed by 
letting the user supply a patch to be committed rather than using the 
files in the current working directory.

commit-patch supports Darcs, Git, Mercurial, Bazaar, Subversion,
Monotone or CVS repositories.

Also included is an Emacs interface to commit-patch. It allows you to 
just hit C-c C-c in any patch buffer to apply and commit only the 
changes indicated by the patch, regardless of the changes in your 
working directory.

WWW: http://www.porkrind.org/commit-patch/