Extension package title collides with OS packages

Affected Puppet, Ruby, OS and module versions/distributions

• Puppet: 4.x
• Ruby: 2.1.5p273
• Distribution: Debian
• Module version: 5.x.x, 4.x.x

How to reproduce (e.g Puppet code you use)

package {['curl', 'memcache']: }

class {'php':
  'extensions' => {
    'curl' => {},
    'memcache' => {
      'provider' => 'pecl',
    }
  }
}

What are you seeing

Error because the package title used for the pecl extension is the same as an OS package we want to install in the same node.

What behaviour did you expect instead

Correct installation of both debian and pecl packages with the same name.

Output log

Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error: Error while evaluating a Resource Statement, Duplicate declaration: Package[curl] is already declared in file ...
Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error: Error while evaluating a Resource Statement, Duplicate declaration: Package[memcache] is already declared in file ...

Start with the extensions resource declarations used by the provided Puppet manifest, especially the curl and memcache PECL entries, and reproduce the duplicate Package declarations on Debian. The change is done when the manifest can install both the OS packages and the same-named PECL extensions without duplicate-resource errors.