Fix lasttag expression to get "latest tag *so far*"

Turns out that the old version has always shown the last tag available
instead of last tag available *so far*, i.e. up to the current HEAD.

This made it impossible to determine version correctly when an older
version was checked out, i.e. installing or packaging an older version
would result in broken versioning.

src/include/build.sh

     grep ":" <<<"$prerl" && warn "colon in PRERELEASE may corrupt version data: $prerl"
     if git rev-parse HEAD >&/dev/null;
     then    # we are in git repo... so we can get smart
-        local lasttag=$(git tag | grep ^v | sort -V | tail -n1)
+        local latest_tag=$(
+            git log --format="%D" \
+              | sed 's/,/\n/g' \
+              | sed 's/^[[:blank:]]*//; ' \
+              | grep -E '^tag: v[[:digit:]]+\.' \
+              | cut -d' ' -f2 \
+              | head -1
+        )
         if ! git describe --tags --exact-match HEAD >&/dev/null;
         then    # we are at a later commit than the last tag
             local sha=g$(git log -1 --pretty=format:%h HEAD)
         then    # the tree is "dirty", i.e. has been edited
             local dirty=dirty
         fi
-        test -n "$lasttag" && version=${lasttag:1}
+        test -n "$latest_tag" && version=${latest_tag:1}
         local suffix=""
         case "$commit:$dirty" in
             :)       suffix=""                ;;