Fix a problem where the PCD decoder overruns the shuffle buffer.

See Pillow bug #568:

  https://github.com/python-pillow/Pillow/issues/568

with their commit at:

  https://github.com/wiredfool/Pillow/commit/ae453aa18b66af54e7ff716f4ccb33adca60afd4

(Pillow is a fork of PIL).

Note that there is no point in pushing the fix upstream to the

PIL community, as that project has been unresponsive. We need

to switch over to using Pillow at some point instead.

--- Imaging-1.1.7/libImaging/PcdDecode.c.orig	2016-02-02 15:45:33.655102971 -0800

+++ Imaging-1.1.7/libImaging/PcdDecode.c	2016-02-02 15:46:00.615105790 -0800

@@ -47,7 +47,7 @@

 	    out[0] = ptr[x];

 	    out[1] = ptr[(x+4*state->xsize)/2];

 	    out[2] = ptr[(x+5*state->xsize)/2];

-	    out += 4;

+	    out += 3;

 	}

 	state->shuffle((UINT8*) im->image[state->y],

@@ -62,7 +62,7 @@

 	    out[0] = ptr[x+state->xsize];

 	    out[1] = ptr[(x+4*state->xsize)/2];

 	    out[2] = ptr[(x+5*state->xsize)/2];

-	    out += 4;

+	    out += 3;

 	}

 	state->shuffle((UINT8*) im->image[state->y],