[vtkusers] libvtkFiltersVerdict-6.3.so.1 vs. libvtkFiltersVerdict.so.6.3

[Nico Schlömer]

On a standard VTK build, I see that the installed libraries are, e.g.,
```
libvtkFiltersVerdict-6.3.so
libvtkFiltersVerdict-6.3.so.1
```
(The first being a symlink to the second.) This looks really odd; I
would have expected
```
libvtkFiltersVerdict.so
libvtkFiltersVerdict.so.6
libvtkFiltersVerdict.so.6.3
```
as is intended by CMake's VERSION and SOVERSION properties.

Any insight here?

Cheers,
Nico