[WIP] add support to open vfs streams with compress.zlib://vfs://path/to/file.txt

[mikey179]

This adds support to open vfs streams using compress.zlib:// as a prefix as described in #121. However, it involves writing to disk as the vfsStream wrapper must return a file resource on its stream_cast method. I tried using php://memory first, but this resulted in a similar error message. Writing to the real file system kind of defeats the purpose of vfsStream of having no file system interaction at all. However, vfsStream could take care of removing such temporary files on its own (not implemented yet), so for the user there would be no difference at all, even though such operations might be a bit slower.

Update: using php://temp works. This solves the problem of having an interaction with the disk - PHP itself will take care of this in case a certain threshold is reached, so vfsStream doesn't have to take care of this. Additionally, this only applies to large files, but most likely not to the overwhelming majority of file sizes in unit tests.

With the current patch, this example code works:

$root = vfsStream::setup("root");
file_put_contents('compress.zlib://vfs://root/test.nbt', 'barbaz');
// displays string(6) "barbaz"
var_dump(file_get_contents('compress.zlib://vfs://root/test.nbt')); 

[staabm]

seems to be unused

[coveralls]

Coverage decreased (-0.03%) to 94.249% when pulling 116f535 on compress_zlib_support into f4aabeb on master.

[mikey179]

Can't even make this work partially with fopen(), having this with file_put_contents() and file_get_contents() only doesn't make sense.