Added Bwana to OS X plugin.

plugins/osx/functions/manb

@@ -0,0 +1,18 @@
+# Open man pages in Bwana.
+function manb() {
+  local page
+  if (( $# > 0 )); then
+    for page in "$@"; do
+      open "man:$page" 2>/dev/null
+      if (( $? != 0 )); then
+        print "$0: Bwana is not installed" >&2
+        break
+      fi
+    done
+  else
+    print 'What manual page do you want?' >&2
+  fi
+}
+compdef _man manb
+manb "$@"
+