R1:42566379dc3c

Fix HTTP body decompression in PHP 5.6

Summary:
Ref T10264. Under PHP 5.6, you are no longer allowed to use `compress.zlib://php://input` as an argument to either `fopen()` or `file_get_contents()`.

Instead, open `php://input` as a file handle, then add `zlib.inflate` as a stream wrapper. This requires some level of magic to work properly.

Test Plan:
First, I constructed a synthetic gzipped payload by typing some words into a file and using `gzcompress()` to compress it.

Then I used a `curl` command…