add build_tests option

[ffontaine]

Allow the user to disable build of test programs

Signed-off-by: Fabrice Fontaine fontaine.fabrice@gmail.com

[kjellahl]

I've merged this PR and added a commit that makes the build_tests check more like the
check in cairomm and libxml++. I've copied the two commits to the libsigc++-2-12 branch.

[ffontaine]

In my first iteration, I tried to set build_by_default as done by commit 5711e2b but for an unknown reason, it wasn't working (the tests were always built). I'll double check on master.

[kjellahl]

Did you put if build_tests around test(ex_name, exe_file)?

  # If exe_file is a test program, it is built by default unconditionally.
  if build_tests
    test(ex_name, exe_file)
  endif

[ffontaine]

Nope, I only updated build_by_default, thanks for your answer.