THRIFT-1482: Unix domain socket support under PHP

[sveneld]

Update tests for this pull request #3109

To open a unix socket, the port number supplied to fsockopen (and pfsockopen) has to be -1.

We use substr instead of str_starts_with to keep compatibility with php 7.

Now a UDS can be created like this:

new TSocket('unix:///tmp/ipc.sock', -1)

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[Jens-G]

Thanks!