Make swallowing more robust

Changed the flags for the pstree command so it is a single line with all
ancestors.
Removed usage of sed, grep and tr so the iopopen call should be faster.
Find and match of parent pid in the ancestors string is done in lua so
should be faster.

module/window_swallowing.lua

@@ -38,16 +38,14 @@ local function manage_clientspawn(c)
     end
 
     -- io.popen is normally discouraged. Should probably be changed
-    local handle = io.popen(
-        [[pstree -T -p -a -s ]]
-            .. tostring(c.pid)
-            .. [[ | sed '2q;d' | grep -o '[0-9]*$' | tr -d '\n']]
-    )
+    -- returns "init(1)---ancestorA(pidA)---ancestorB(pidB)...---process(pid)"
+    local handle = io.popen("pstree -A -p -s " .. tostring(c.pid))
     local parent_pid = handle:read("*a")
     handle:close()
 
     if
-        (tostring(parent_pid) == tostring(parent_client.pid))
+        -- will search for "(parent_client.pid)" inside the parent_pid string
+        ( tostring(parent_pid):find("("..tostring(parent_client.pid)..")") )
         and check_if_swallow(c)
     then
         c:connect_signal("unmanage", function()