Fixed Request #66574 Allow multiple paths in php_ini_scanned_path

php_ini_scanned_path, from --with-config-file-scan-dir option or
from PHP_INI_SCAN_DIR environment variable allow a single path.

In some case it could be useful to allow multiple.

In the proposed patch, multiple paths are allow, using syntax inspired
from Unix MANPATH (: separated list, empty string for builtin value).

For example, this allow to use:
PHP_INI_SCAN_DIR=/foo/php.d:/bar/php.d   php
PHP_INI_SCAN_DIR=:/myproject/php.d       php
PHP_INI_SCAN_DIR=/myproject/php.d:       php

Real use case: in SCL for dependent collections where each collection
provides a separate tree for extensions, libraries and ini files.
Merge branch 'PHP-5.5' into PHP-5.6

* PHP-5.5:
  Fixed Request #66574 Allow multiple paths in php_ini_scanned_path