shim: Add basic button support

tests/examples/shims/_common_template.lua

@@ -1,7 +1,7 @@
 return function(_, _, luacovpath)
 
     -- Set the global shims
-    -- luacheck: globals awesome root tag screen client mouse drawin
+    -- luacheck: globals awesome root tag screen client mouse drawin button
     awesome = require( "awesome" )
     root    = require( "root"    )
     tag     = require( "tag"     )
@@ -9,6 +9,7 @@ return function(_, _, luacovpath)
     client  = require( "client"  )
     mouse   = require( "mouse"   )
     drawin  = require( "drawin"  )
+    button  = require( "button"  )
 
     -- Force luacheck to be silent about setting those as unused globals
     assert(awesome and root and tag and screen and client and mouse)

tests/examples/shims/button.lua

@@ -0,0 +1,3 @@
+return function() return {
+    connect_signal = function() end
+} end