Don't use const

The behaviour is unreliable in Spidermonkey 1.8.5, and the behaviour
will change based on JS options.

exec/tests/global/format.js

-const args = [ 1, 1.1, true, "one", -1, 1e9, null, undefined ];
+var args = [ 1, 1.1, true, "one", -1, 1e9, null, undefined ];
 
-const test = {
+var test = {
 	"%s":		"1",
 	"%d":		"1",
 	"%i":		"1",

exec/tests/user/birthdate.js

 // This test requires Synchronet v3.20c or later to pass
 
-const test = {
+var test = {
 	"50 ":		"19500101",
 	"60.1":		"19600101",
 	"69e1":		"19690101",