[FYI] merged maint into master

[Stefano Lattarini]

I merged maint into master, and pushed.

The merged commits are:
 - Ralf Wildenhues (1):
     Fix and document rules to not touch the tree with `make -n'.
 - Stefano Lattarini (1):
     Fix bug in rules for creating vala vapi/header files.

Regards,
  Stefano