[barcode] DESTDIR support patch for GNU barcode

[Alessandro Rubini]

> 
> INFO = $(TARGET).info
> $(INSTALL) -c -m 0644  doc/$(INFO) $(DESTDIR)$(INFODIR)/$(INFO)

I'll use basename instead. These new compliance rules are breaking
things: I want to name a file in a variable and then copying it
without any concern about the pathname of that file.

The way you suggest makes the INFO variable unuseful. The point
of setting variables at the beginning of the file is in recycling
the same makefile across packages, and this is breaking it.
Needless to say, I don't like $(MAN1DIR)/$(MAN1), either.

However, we'll stick to the rules. 

/alessandro