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