Implement persistent plain file streams.

Implement persistent plain file streams.

Usage:

php_stream *stream = php_stream_fopen("/path/to/file", "r+b", NULL,
	STREAM_OPEN_PERSISTENT | ENFORCE_SAFE_MODE | REPORT_ERRORS);

the filename and mode are combined to form the hash key for the persistent
list; they must be identical for this same stream to be returned again in the
next request.

Calling php_stream_close() on a persistent stream *will* close it, as is
usual with all persistent resources in PHP/ZE.

This is deliberately *not* exposed to user-space PHP at this time.