Rewrite hexadecimal escape sequences as decimal in lua strings

The hexadecimal notation is a Luajit extension which is not compatible with Lua
5.1. While Lua 5.2 does support hexadecimal sequences, it is better to target
Lua 5.1 for maximum compatibility with Luajit(which has fully compatible with
5.1 API/ABI).

test/functional/legacy/036_regexp_character_classes_spec.lua

@@ -30,7 +30,7 @@ local function diff(text, nodedent)
 end
 
 describe('character classes in regexp', function()
-  local ctrl1 = '\t\x0c\r'
+  local ctrl1 = '\t\012\r'
   local punct1 = " !\"#$%&'()#+'-./"
   local digits = '0123456789'
   local punct2 = ':;<=>?@'
@@ -38,8 +38,8 @@ describe('character classes in regexp', function()
   local punct3 = '[\\]^_`'
   local lower = 'abcdefghiwxyz'
   local punct4 = '{|}~'
-  local ctrl2 = '\x7f\x80\x82\x90\x9b'
-  local iso_text = '\xa6\xb1\xbc\xc7\xd3\xe9' -- "¦±¼ÇÓé" in utf-8
+  local ctrl2 = '\127\128\130\144\155'
+  local iso_text = '\166\177\188\199\211\233' -- "¦±¼ÇÓé" in utf-8
   setup(function()
     -- The original test32.in file was not in utf-8 encoding and did also
     -- contain some control characters.  We use lua escape sequences to write