dependency system: better use "-include"

[Thomas Langen]

The decision to make the dependency system include dependency files by 
the command "include $(DEPDIR)/Desktop.Po" or alike has an ugly 
side-effect: For project management systems these dependency files are 
typically not stored so checking out the source tree leaves it without 
them. Then, for the first run, this results in warnings claiming that 
these files are missing. I suggest the following fixes:

1. use the "silent inclusion" sinclude or -include instead of include, 
then these files are just ignored if missing

2. have a rule to automatically touch (create) these dependency headers 
if they are missing - they do not cause any harm if empty, and they will 
get updated on compiler runs.

--
Thomas Langen
address@hidden