Ported r2996 from ZXing

Original commit message: "Issue 1823: fix handling of initial alt
Codabar char, and improve tests"
Ported r3000 from ZXing

Original commit message: "Handle smaller images in
WhiteRectangleDetector"
Ported r3001 from ZXing

Original commit message: "Issue 1825. PDF417Reader can't modify the
image. When it doesn't, it actually reduces the number of images that
pass unfortunately."