Versioning of Linux shared objects, and OSX dylibs

[markfinal]

Linux requires a number of symbolic links to be set up.

OSX requires some linker options.

Needs to be Bam settings to configure these values. Additional work on Linux required to generate the symbolic links.

Windows is separate, as DLL versioning is done in resource files.

[markfinal]

Note that VisualC link.exe does have a -VERSION:major.minor option. But this is just embedded into the executable, and not queryable from Windows Explorer - a resource file is still needed for that.