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.
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