How to enable mhash

[gpsa]

I already enabled hash extension on php:5.6-apache image and installed libmhash-dev, but it doesn't enable mhash.
In PHP doc. page:

As of PHP 5.3.0, the mhash extension is emulated thru the Hash extension. This makes the mhash installation directory have no effect, and requires the hash extension enabled to make the mhash support available.

But even though it doesn't enable mhash functions

[tianon]

Sorry for the delay!

It would appear that PHP includes --enable-hash by default, but that does not include --with-mhash by default, and it's very difficult to get it working after-the-fact. The closest I got was by installing libmhash-dev, and using docker-php-ext-configure hash --with-mhash=/usr followed by docker-php-ext-install hash, but then it doesn't get enabled because it's already enabled in the core by default (and PHP won't load it a second time).

I think we either need to bake --with-mhash into the image itself (which I'm not too fond of), or use --disable-hash so that it can be compiled and installed successfully after-the-fact instead (which is the solution I'd be more partial to, although it obviously requires testing to ensure that my proposed solution actually works).

[tianon]

Finally got around to testing this, and --disable-hash allowed me to successfully do docker-php-ext-configure hash --with-mhash followed by docker-php-ext-install hash. 👍

See #627. 🤘