Allow using ctrl-[ to drill down into man pages, when using man-db

--- /usr/share/vim/vim73/ftplugin/man.vim	2010-11-29 10:00:14.392636934 +0000
+++ man.vim	2010-11-29 10:00:07.233636869 +0000
@@ -15,6 +15,10 @@
   endif
   let b:did_ftplugin = 1
 
+  "Ensure vim is not recursively invoked (man-db does this)
+  "when doing ctrl-[ on a man page reference
+  let $MANPAGER=""
+
   " allow dot and dash in manual page name.
   setlocal iskeyword+=\.,-