CMake warnings

[ricortiz]

There are several warnings concerning not used variables passed to the external projects.

[ricortiz]

For CTK:
CMake Warning:
Manually-specified variables were not used by the project:

GIT_EXECUTABLE

...

DOCUMENTATION_ARCHIVES_OUTPUT_DIRECTORY
DOCUMENTATION_TARGET_IN_ALL

For MSVTK:
CMake Warning:
Manually-specified variables were not used by the project:

DOCUMENTATION_ARCHIVES_OUTPUT_DIRECTORY