[cmake-developers] Review Request for ExternalProjects: Only update certain git submodules

[Gereon Kremer]

Hi,

When using external projects from git repositories that have many large 
submodules (for example boost), one might want to clone and update only 
a certain set of submodules.
The attached patch implements this features by a new option GIT_SUBMODULES.

Cheers,
Gereon

PS: As this is my first CMake patch, I don't have any (write) access to 
the git and thus simply attached the patch to this mail.

-- 
Gereon Kremer
Lehr- und Forschungsgebiet Theorie Hybrider Systeme
RWTH Aachen
Tel: +49 241 80 21242