Merge pull request #1 from stanley-cheung/support_php7_by_marco

src/php/ext/grpc/channel.c

src/php/ext/grpc/channel_credentials.c

src/php/ext/grpc/server_credentials.c

src/php/ext/grpc/timeval.c

src/php/tests/unit_tests/CallCredentialsTest.php

src/php/tests/unit_tests/CallTest.php

src/php/tests/unit_tests/ChannelCredentialsTest.php

src/php/tests/unit_tests/ChannelTest.php

src/php/tests/unit_tests/EndToEndTest.php

src/php/tests/unit_tests/ServerTest.php