RFR: Allow using a system installed libpng

[Magnus Ihse Bursie]

On 2014-02-03 21:44, Omair Majid wrote:
> Whoops. Updated webrevs:
> root: http://cr.openjdk.java.net/~omajid/webrevs/system-libpng/02/
> jdk: http://cr.openjdk.java.net/~omajid/webrevs/system-libpng/02-jdk/
>
>> Due to this, I'd like to ask you to please double check that
>> --with-libpng=system | bundled | invalid-value | <empty>, and no
>> flag at all, all work as expected.
> I re-ran all these 4 options. system builds with system, bundled and
> <empty> build a bundled copy and invalid-value fails during configure.
Great, thank you. The fix looks good.

/Magnus