Update stack size in tests/func/010.phpt

Stack size is 16K nowadays. Now the test takes a more reasonable
amount of time to run...

Author: nikic

tests/func/010.phpt

@@ -8,7 +8,7 @@ if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
 <?php
 
 // the stack size + some random constant
-$boundary = 64*1024;
+$boundary = 16*1024-16;
 $limit    = $boundary+42;