fpassthru buggy

fpassthru does not work correctly if the function fgets is called before fpassthru.
Also fpassthru does not increment the ftell position like php does.

Steps to reproduce:

zerotens@zero:/ vi test.php

```
#!/usr/bin/env php
%d\n", a());
```

zerotens@zero:/ # hhvm --version

```
HipHop VM 3.6.1 (rel)
Compiler: tags/HHVM-3.6.1-0-gc051feff88ba8050f33f10f7b1fb07f8d3415f9e
Repo schema: 42f49251b5c27daf4e13cb6bcd0c7ef4824b55a3
```

zerotens@zero:/ # php test.php

```
first line
second line
third line

Result function a() => 35
```

zerotens@zero:/ # hhvm test.php

```

Result function a() => 1

```