Alternative compilation fix for Solaris

Instead of explicitly adding special cases for the Solaris Studio compiler, as proposed in #146, this pull-request addresses the issue from a different angle.

First, the packing `#pragma` is dropped altogether from the `GenericValue` struct.  Even if the compiler decides to add additional padding, this would help for the small-string optimisation and the compiler might have good reasons for that anyhow (e.g. better performance due to better alignment).

Secondly, Sun Studio is known to have quite strict C++ header implementations for the C standard functions (`<cstdlib>`, `cstring>`).  On this implementation, the functions are not automatically exported to the global namespace.  Use explicit `std::` namespace qualifiers instead of including the plain C headers.