[tz] Wrong symlinks with BACKWARD=backward PACKRATDATA=backzone

[Benjamin Drung]

Hi,

the Debian/Ubuntu package uses BACKWARD=backward PACKRATDATA=backzone.
The resulting tzdata.zi has the timezone Africa/Asmara, but
Africa/Asmera points to Africa/Nairobi instead of the existing
Africa/Asmara:

```
$ make AWK=gawk BACKWARD="backward" PACKRATDATA=backzone PACKRATLIST=zone.tab VERSION_DEPS= tzdata.zi
gawk \
	  -v DATAFORM=`expr main.zi : '\(.*\).zi'` \
	  -v PACKRATDATA='backzone' \
	  -v PACKRATLIST='zone.tab' \
	  -f ziguard.awk \
	  africa antarctica asia australasia  europe northamerica southamerica etcetera factory backward backzone >main.zi.out
mv main.zi.out main.zi
{ (type git) >/dev/null 2>&1 && \
	  V=`git describe --match '[0-9][0-9][0-9][0-9][a-z]*' \
			--abbrev=7 --dirty` || \
	  if test 'unknown' = unknown && V=`cat version`; then \
	    case $V in *-dirty);; *) V=$V-dirty;; esac; \
	  else \
	    V='unknown'; \
	  fi; } && \
	printf '%s\n' "$V" >version.out
mv version.out version
version=`sed 1q version` && \
	  LC_ALL=C gawk \
	    -v dataform='main' \
	    -v deps='ziguard.awk africa antarctica asia australasia  europe northamerica southamerica etcetera factory backward backzone zone.tab zishrink.awk' \
	    -v redo='posix_right' \
	    -v version="$version" \
	    -f zishrink.awk \
	    main.zi >tzdata.zi.out
mv tzdata.zi.out tzdata.zi
$ grep Asmera tzdata.zi 
L Africa/Nairobi Africa/Asmera
```

Can this fixed/configured?

-- 
Benjamin Drung
Debian & Ubuntu Developer