Avoid excessive name pollution in test files

Test files are more polite regarding the use of globals when locals
would do, and when globals are necessary deleting them after use.

testes/locals.lua

@@ -37,7 +37,7 @@ end
 f = nil
 
 local f
-x = 1
+local x = 1
 
 a = nil
 load('local a = {}')()
@@ -152,7 +152,7 @@ local dummy
 local _ENV = (function (...) return ... end)(_G, dummy)   -- {
 
 do local _ENV = {assert=assert}; assert(true) end
-mt = {_G = _G}
+local mt = {_G = _G}
 local foo,x
 A = false    -- "declare" A
 do local _ENV = mt
@@ -174,6 +174,8 @@ do local _ENV = {assert=assert, A=10};
 end
 assert(x==20)
 
+A = nil
+
 
 do   -- constants
   local a<const>, b, c<const> = 10, 20, 30
@@ -711,7 +713,7 @@ if rawget(_G, "T") then
 
     collectgarbage(); collectgarbage()
 
-    m = T.totalmem()
+    local m = T.totalmem()
     collectgarbage("stop")
 
     -- error in the first buffer allocation