* CTest must use proper paths to executables

With the following syntax:

```
  add_test(NAME <name> COMMAND <command> [<arg>...])
```

if `<command>` specifies an executable target it will automatically
be replaced by the location of the executable created at build time.

This is important if a `<Configuration>_POSTFIX` like `_d` is used.

* Fix typo in ctest invocation

Instead of `-c` the uppercase `-C` must be used to select a config.
But better use the longopt.