Fix and update docstrings

dotfiles/imapdomo/common.lua

 
 function init_host(session)
     --
-    -- Look for action handler in basepaths; do first one
+    -- Do host-specific init, if exists
     --
     local init = session.dirs.host .. "/init.lua"
     if file_exists(init) then
 
 function handle(session)
     --
-    -- Look for action handler in basepaths; do first one
+    -- Look for action handler in session dirs; do first one that exists
     --
     local valid = {
         newmail = true,