[tex-live] please update to libpng 1.6.2

[Karl Berry]

    [latest libpng] and the comments following, however, it seems that
    some action on the pdftex side is probably necessary also...

Not practical at this point.

    Alternatively, we might stay with libpng 1.5.16...

Almost as bad.  

   [mpost distortion bug]

In the future, evidently I will have to abjectly beg you to test earlier
than two days before the purported deadline, maybe even test Taco's
releases independent of TL, since it's obvious that you are trying many
things that no one else does.  (Not surprising, given Lilypond's needs,
et al.)  Code does not become "production-ready" via random miracles;
people have to actually use it.

Anyway, while these problems you've found are serious and it would
certainly be desirable to fix them ... Peter is away until June 1, and I
am going to be away tomorrow (Friday) through Sunday.  I doubt anyone
else is going to be up for changing the libpng source.

Worse, even after the code is changed, another set of builds is
required, likely inducing new problems, etc.  And soon more crucial
people are going on vacation.  It is hard to say when or if the release
could ever be finished if we delay to fix these things.
   
I see no good choices available.  Guess I'll see what has developed, or
not, when I'm back and we'll have to go from there.

Best,
k