jpeg: update to 9c.

Version 9c  14-Jan-2018
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jpegtran: add an option to the -wipe switch to fill the region
with the average of adjacent blocks, instead of gray out.
Thank to Caitlyn Feddock and Maddie Ziegler for inspiration.

Make range extension bits adjustable (in jpegint.h).
Thank to Robin Watts for suggestion.

Provide macros for fflush() and ferror() in jinclude.h in order
to facilitate adaption by applications using an own FILE class.
Thank to Gerhard Huber for suggestion.

Add libjpeg pkg-config file.  Thank to Mark Lavi, Vincent Torri,
Patrick McMunn, and Huw Davies for suggestion.

Add sanity checks in cjpeg image reader modules.
Thank to Bingchang, Liu for reports.

(wiz)