bootstrap: .gitignore files created by autopoint, libtool

bootstrap: .gitignore files created by autopoint, libtool

I ran into this problem when bootstrapping the latest diffutils.
After './bootstrap', 'git status' reported lots of untracked files
m4/codeset.m4, m4/gettext.m4, etc.  These files were created by
autopoint and do not need to be version-controlled.
* build-aux/bootstrap: Put into .gitignore the files that
autopoint and libtool create, by keeping track of files that exist
after but not before these programs are run.
(version_controlled_file): Move up.  2nd arg is now full file
name, not base name; this is more convenient.  Put CVS at the end,
as it's now somewhat deprecated.