fixed alternate form for 'x' and 'X' formats

same fix exists in original code:
https://svn.apache.org/viewvc?view=revision&revision=1152309
Merge branch 'PHP-5.4' into PHP-5.5
different OSes have different messages, and that's not what the test is about anyway
fix bug #63982: isset() inconsistently produces a fatal error on protected property
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  fix bug #63982: isset() inconsistently produces a fatal error on protected property
  different OSes have different messages, and that's not what the test is about anyway
Tinker with UPGRADING's wording for the format string changes for clarity.