Bugfix#75515 php://streams behaving greedily

Bugfix#75515 php://streams behaving greedily

5060fc23 attempted to fix #68948 by treating all non-uri streams
as non-blocking, however php://fd/* streams (which includes stdin)
may block if the other end of the IPC isn't finished.

This represents a partial revert to the pre RC6 state,
but includes an escape hatch for php://memory and php://temp
streams which are local to the current process.

This also restores stream_set_chunk_size test to previous state.