bash: Replace 'cp -d' command with POSIX 'cp -P'

Comment from Eric Blake:

> We don't have any hard-links in our source. GNU cp -d is the same as
> cp -P --preserve=links, but --preserve=links only matters for hard
> links, so losing it doesn't hurt our usage. I'm inclined to just go
> with cp -P unconditionally rather than needing the configure.ac
> logic for $(CP_D).

Fixes: libguestfs/libguestfs#183
Reported-by: Mohamed Akram
Thanks: Eric Blake

(cherry picked from
libguestfs commit e49d65a5fd07e40260e800c0c262dad7e367b2f6)

Author: rwmjones

bash/Makefile.am

@@ -74,7 +74,7 @@ all-local: $(scripts) $(symlinks)
 
 install-data-local:
 	$(mkdir_p) $(DESTDIR)$(bashcompletiondir)
-	cp -d $(scripts) $(symlinks) $(DESTDIR)$(bashcompletiondir)
+	cp -P $(scripts) $(symlinks) $(DESTDIR)$(bashcompletiondir)
 
 clean-local:
 	-test $(srcdir) != $(builddir) && rm -f $(scripts)