func canSkip(p pkgEntry, vPath string) bool {
	v, err := ioutil.ReadFile(vPath)
	if err != nil {
		return false
	}
	vCurrent, err := version.Parse(string(v))
	if err != nil {
		log.Printf("Warning: could not parse current package version from %q: %v", vPath, err)
		return false
	}
	return version.Compare(vCurrent, p.version) >= 0
}
canSkip returns true if the package is present in the same (or a
newer) version on disk already.
package main
import (
	"archive/tar"
	"bufio"
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync/atomic"
	"unicode/utf8"
	"golang.org/x/net/context"
	"golang.org/x/sync/errgroup"
	"github.com/Debian/debiman/internal/manpage"
	"github.com/Debian/debiman/internal/recode"
	"github.com/Debian/debiman/internal/write"
	"pault.ag/go/archive"
	"pault.ag/go/debian/control"
	"pault.ag/go/debian/deb"
	"pault.ag/go/debian/version"
)