Fix some warnings in MSVC 2015

[ianhbell]

  C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(175): warning C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data [C:\Users\ih
b\Documents\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\Backends\Helmholtz\HelmholtzEOSMixtureBackend.cpp(2424): warning C4101: 'e': unreferenced local variable [C:\Users\ihb\Documents\Code\Co
olProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\Backends\Helmholtz\MixtureParameters.cpp(672): warning C4244: '=': conversion from 'long' to 'short', possible loss of data [C:\Users\ih
b\Documents\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\Backends\Helmholtz\MixtureParameters.cpp(673): warning C4244: '=': conversion from 'long' to 'short', possible loss of data [C:\Users\ih
b\Documents\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\Backends\Helmholtz\MixtureParameters.cpp(674): warning C4244: '=': conversion from 'long' to 'short', possible loss of data [C:\Users\ih
b\Documents\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\Backends\Helmholtz\MixtureParameters.cpp(675): warning C4244: '=': conversion from 'long' to 'short', possible loss of data [C:\Users\ih
b\Documents\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\include\miniz.h(1453): warning C4334: '<<': result of 32-bit shift implicitly converted to 64 bits (was 64-bit shift intended?) [C:\Users\ih
b\Documents\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\ODEIntegrators.cpp(12): warning C4267: 'initializing': conversion from 'size_t' to 'long', possible loss of data [C:\Users\ihb\Documents
\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\ODEIntegrators.cpp(12): warning C4267: 'initializing': conversion from 'size_t' to 'const long', possible loss of data [C:\Users\ihb\Doc
uments\Code\CoolProp\build\dll\CoolProp.vcxproj]
  C:\Users\ihb\Documents\Code\CoolProp\src\ODEIntegrators.cpp(191): warning C4503: 'Eigen::MatrixBase<Derived>::operator +': decorated name length exceeded, name was truncated [C:
\Users\ihb\Documents\Code\CoolProp\build\dll\CoolProp.vcxproj]

[ianhbell]

First warning arrives from:

3>  C:\Users\ihb\Documents\NIST\Papers\In Progress\PsychMix (BERB)\code\externals\CoolProp\src\Backends\Cubics\UNIFAQ.cpp(133): note: see reference to function template instantiation 'std::pair<int,int>::pair<size_t&,size_t&,void,0>(_Other1,_Other2) noexcept' being compiled
3>          with
3>          [
3>              _Other1=size_t &,
3>              _Other2=size_t &
3>          ]
3>  C:\Users\ihb\Documents\NIST\Papers\In Progress\PsychMix (BERB)\code\externals\CoolProp\src\Backends\Cubics\UNIFAQ.cpp(133): note: see reference to function template instantiation 'std::pair<int,int>::pair<size_t&,size_t&,void,0>(_Other1,_Other2) noexcept' being compiled
3>          with
3>          [
3>              _Other1=size_t &,
3>              _Other2=size_t &
3>          ]