Git submodules

[David Edmundson]

I tried updating the contact list to use the git submodule
telepathy-common-internals

It mostly went smoothly but I have two issues:

If I ship as-is people need to run "git submodule init" "git submodule
update" before their code will compile.

I tried adding it into CMakeFiles.txt as
execute_process(COMMAND git update blah blah blah WORKING_DIRECTORY
${CMAKE_SRC_DIR} )

This works, but only when they run cmake twice, the first time it
errors that the cpp files (from the submodule) aren't there before
running my execute line. The second time it's fine.
No idea why.

Also - it's going to completely break making tarballs.
I assume it makes sense for the tarballs to have the code for the git
sub-repo in part of the tarball. This means my cmake line to run "git
submodule init" etc. will break everything.

I'm not sure how to do this in a way that's nice for normal users, and
isn't going to make every packager want to murder me.

Dave