Fix bug in dep resolution when requesting a "const T*"

[J-Meyers]

Duplicate of #347

Hello,
I have fixed a bug in dependency resolution when requesting a "const T*" after injecting a "T*" as dependency.

Before this fix, if a T* was injected as dependency, requesting a const T* will result in a invalid nullptr.
The dependency resolution of objects passed by reference is not affected by this problem.

I have added four tests:

dependencies_with_reference
dependencies_with_const_reference
dependencies_with_pointer
dependencies_with_const_pointer (this test fails without the fix)
I am new to TMP and this is my first contribute in general so I hope I didn't do anything wrong.

I recently encountered this same issue, figured I'd resolve any merge conflicts so that it's able to be merged in.