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 like this to make requests with it:

```
$ curl -X POST -H "Content-Length: 66" -H "Content-Type: text/plain" -H "Content-Encoding: gzip" --data-binary @payload.deflate -v http://127.0.0.1/
```

I modified Phabricator to just dump the raw request body and exit, and reproduced the issue under PHP 5.6 (no body, error in log) by brining up a micro instance in EC2 and installing php56 on it.

After this patch, it dumped the body properly instead, and PHP 5.5 also continued worked properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10264

Differential Revision: https://secure.phabricator.com/D15314