Add test for #1259

tests/template/tscope.nim

@@ -0,0 +1,12 @@
+discard """
+  errormsg: "redefinition of 'x'"
+"""
+
+var x = 1
+template quantity(): stmt {.immediate.} =
+  # Causes internal error in compiler/sem.nim
+  proc unit*(x = 1.0): float = 12
+  # Throws the correct error: redefinition of 'x'
+  #proc unit*(y = 1.0): float = 12
+quantity()
+var x = 2