This reverts commit eef85229d0fe9f69d325aa0231e592f35c468afb.

The meaning of the limit changed in 7.4, it now points one past the
end. Adjust code accordingly.

This reverts commit e0eca262852dba1a78afcde64a49126c81fead1a.

free_filename is used by the wincache extension, restore this
field for PHP 7.4.

The php_stream_read() and php_stream_write() functions now return
an ssize_t value, with negative results indicating failure. Functions
like fread() and fwrite() will return false in that case.

As a special case, EWOULDBLOCK and EAGAIN on non-blocking streams
should not be regarded as error conditions, and be reported as
successful zero-length reads/writes instead. The handling of EINTR
remains unclear and is internally inconsistent (e.g. some code-paths
will automatically retry on EINTR, while some won't).

I'm landing this now to make sure the stream wrapper ops API changes
make it into 7.4 -- however, if the user-facing changes turn out to
be problematic we have the option of clamping negative returns to
zero in php_stream_read() and php_stream_write() to restore the
old behavior in a relatively non-intrusive manner.

Disable buffering in PHP streams, to avoid storing and copying the
file contents twice.

This will call stream_set_option() on custom stream wrapper as
well, so the method needs to be implemented to avoid a warning.

The buf/len members are now simply used in addition to the main
stream, without changing the handle kind.

free_filename was always zero.