Minor bugfix: Added missing composer dependency (ServiceManager) to Math package

[dol]

The Zend\Math package uses the ServiceManager. But the composer.json requirements don't define this dependency.
This PR fixes this issue.

[samsonasik]

I think it should be on 'suggest' dependency. We still can use Zend\Math\BigInteger\Adapter\Bcmath directly.

[dol]

I agree, that you could use Zend\Math\BigInteger\Adapter\Bcmath directly. The convenience of BigIntiger::factory() and the build-in Zend\ServiceMangager\AbstractPluginManager is that you don't have to decide witch adapter to use.
Without the ServiceManager dependency I have to duplicate the code of decision making of using Zend\Math\BigInteger\Adapter\Bcmath or Zend\Math\BigInteger\Adapter\Gmp.
I'd like to use this package for a math project and I don't want to deal with different calculation adapters. The missing dependency blocks me from using this package.
The examples in the ZF2 documentation won't work out of the box without the ServiceManager.

I would rather add ext-bcmath and ext-gmp (e.g) to the 'suggest' section.

Btw:
There was recently a poll on the composer-dev mailinglist about the 'suggest' section and when to display.

[samsonasik]

ok, so it up to the zf maintainer to agree or not :). btw, i think 'component' is the better word than 'module' :D

[dol]

@samsonasik Thanks you for the critics about this issue. A second opinion is always good. btw: I changed the title from 'module' to 'package' due the naming taken from here.

[weierophinney]

@dol I agree with @samsonasik here -- this is a suggested dependency, not a required dependency, as you can use selected functionality from the component without the ServiceManager package installed. While I understand that the examples in the doc will not work without the SM, the documentation also typically assumes you've installed the entire framework.

Change the package to a suggestion, and add in the string "if using the BigInteger::factory functionality". I'd also add "ext-bcmath" and "ext-gmp" as suggestions.