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/gc.lua

@@ -125,7 +125,7 @@ do
   end
 
   a:test()
-
+  _G.temp = nil
 end
 
 
@@ -134,7 +134,7 @@ do local f = function () end end
 
 
 print("functions with errors")
-prog = [[
+local prog = [[
 do
   a = 10;
   function foo(x,y)
@@ -153,22 +153,25 @@ do
     end
   end
 end
+rawset(_G, "a", nil)
+_G.x = nil
 
-foo = nil
-print('long strings')
-x = "01234567890123456789012345678901234567890123456789012345678901234567890123456789"
-assert(string.len(x)==80)
-s = ''
-k = math.min(300, (math.maxinteger // 80) // 2)
-for n = 1, k do s = s..x; j=tostring(n)  end
-assert(string.len(s) == k*80)
-s = string.sub(s, 1, 10000)
-s, i = string.gsub(s, '(%d%d%d%d)', '')
-assert(i==10000 // 4)
-s = nil
-x = nil
+do
+  foo = nil
+  print('long strings')
+  local x = "01234567890123456789012345678901234567890123456789012345678901234567890123456789"
+  assert(string.len(x)==80)
+  local s = ''
+  local k = math.min(300, (math.maxinteger // 80) // 2)
+  for n = 1, k do s = s..x; local j=tostring(n)  end
+  assert(string.len(s) == k*80)
+  s = string.sub(s, 1, 10000)
+  local s, i = string.gsub(s, '(%d%d%d%d)', '')
+  assert(i==10000 // 4)
 
-assert(_G["while"] == 234)
+  assert(_G["while"] == 234)
+  _G["while"] = nil
+end
 
 
 --
@@ -227,8 +230,8 @@ end
 
 
 print("clearing tables")
-lim = 15
-a = {}
+local lim = 15
+local a = {}
 -- fill a with `collectable' indices
 for i=1,lim do a[{}] = i end
 b = {}
@@ -552,6 +555,7 @@ do
     for i=1,1000 do _ENV.a = {} end   -- no collection during the loop
   until gcinfo() > 2 * x
   collectgarbage"restart"
+  _ENV.a = nil
 end