awful.util: add table.clone

This is useful because tables get passed by reference instead of by
value, so we might end up modifying tables where we don't want it.

Signed-off-by: Gregor Best <farhaven@googlemail.com>
Signed-off-by: Julien Danjou <julien@danjou.info>

lib/awful/util.lua.in

@@ -334,4 +334,15 @@ function table.reverse(t)
     return tr
 end
 
+--- Clone a table
+-- @param t the table to clone
+-- @return a clone of t
+function table.clone(t)
+    local c = { }
+    for k, v in pairs(t) do
+        c[k] = v
+    end
+    return c
+end
+
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