Bug #66481 Segfaults on session_name()

If the previous value of session.name was NULL then any call to
session_name($string) would result in a segmentation fault.

This changes the behaviour to set the value of session.name to
"PHPSESSID" if a blank value is given in php.ini or via -d on the
command line. There is already protection against setting it to NULL via
session_name() or ini_set().
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  Bug #66481 Segfaults on session_name()
Merge branch 'PHP-5.5' into PHP-5.6

* PHP-5.5:
  Bug #66481 Segfaults on session_name()
Merge branch 'PHP-5.6'

* PHP-5.6:
  Bug #66481 Segfaults on session_name()
Update NEWS
Update NEWS
Revert "Update NEWS"

This reverts commit 8f5de8ddcf5fea43928cf2358b95f3de1ab5ade9.
Revert "Bug #66481 Segfaults on session_name()"

This reverts commit 5662ffb295c6f9cb10768d8246f2656aae6b8abb.
Re-fixed Bug #66481 (Calls to session_name() segfault when session.name is null)
Merge branch 'PHP-5.4' into PHP-5.5
Merge branch 'PHP-5.5' into PHP-5.6
Merge branch 'PHP-5.6'