add working CVS plugin

diff --git a/doc/plugins/contrib/cvs.mdwn b/doc/plugins/contrib/cvs.mdwn
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+[[!template id=plugin name=cvs core=0 author="[[schmonz]]"]]
+
+This plugin allows ikiwiki to use [[!wikipedia desc="CVS" Concurrent Versions System]] as an [[rcs]].
+
+* Diffs are against [[3.14159|news/version_3.14159]]. `cvs.pm` started life as a copy of `svn.pm`.
+* `IkiWiki.pm` avoids copying CVS metadata into `$DESTDIR`.
+* [[ikiwiki-makerepo]]:
+ * creates a repository,
+ * imports `$SRCDIR` into top-level module `ikiwiki` (vendor tag IKIWIKI, release tag PRE_CVS),
+ * creates a small post-commit wrapper to prevent `cvs add <directory>` from being seen by ikiwiki's [[post-commit]] hook,
+ * configures the wrapper itself as a post-commit hook in `CVSROOT/loginfo`.
+* [`cvsps`](http://www.cobite.com/cvsps/) is required (`rcs_recentchanges()` and `rcs_diff()` need it to work).
+* CVS multi-directory commits happen separately; the post-commit hook sees only the first directory's changes in time for [[recentchanges|plugins/recentchanges]]. The next run of `ikiwiki --setup` will correctly re-render such a recentchanges entry. It might be possible to solve this problem with scripts like `commit_prep` and `log_accum` from CVS contrib.
+* Due to the name of CVS's metadata directories, it's impossible to create `.../CVS/foo.mdwn`. On case-insensitive filesystems it's also impossible to create `.../cvs/foo.mdwn`.
+* No testing or special-casing has been done with [[attachments|plugins/attachment]], but they'll probably need `cvs add -kb`.
+
+Having a `$HOME/.cvsrc` isn't necessary. Sure does make using CVS more livable, though. Here's a good general-purpose one:
+
+    cvs -q
+    checkout -P
+    update -dP
+    diff -u
+    rdiff -u
+
+Not knowing how the tests get set up, I blindly attempted to add subversion-like tests to `t/file_pruned.t`. They fail. But the plugin definitely works. :-)
+
+### Code
+* [`cvs.pm`](http://www.netbsd.org/~schmonz/ikiwiki-cvs/cvs.pm)
+* [`cvs-IkiWiki.pm.diff`](http://www.netbsd.org/~schmonz/ikiwiki-cvs/cvs-IkiWiki.pm.diff)
+* [`cvs-ikiwiki-makerepo.diff`](http://www.netbsd.org/~schmonz/ikiwiki-cvs/cvs-ikiwiki-makerepo.diff)
+* [`cvs-t-file_pruned.t.diff`](http://www.netbsd.org/~schmonz/ikiwiki-cvs/cvs-t-file_pruned.t.diff)