Updates for new year.
coders/png.c: Use png_scale_16_to_8() in preference to png_scale_16_to_8()

so ref tests don't fail due to the slightly more accurate downscaling.
coders/png.c: Don't use any libpng functions to scale 16-bit input down

to 8-bit, to obtain the same behavior of PNG as with other formats.
coders/png.c: Use png_set_strip_16_to_8, not png_set_scale_16_to_8 with Q8

builds, to prevent small differences from causing reference test failures.
ChangeLog: mention fallback on png_set_scale_16_to_8() when
png_set_strip_16_to_8() is not supported.
coders/png.c added a comment
coders/png.c: added test for PNG_READ_16_TO_8_SUPPORTED which is needed

when building Q8 with libpng 1.4.x and earlier.
Fix PerlMagick input_16.png signatures.
Added Wand API MagickSetImageGravity() and MagickGetImageGravity().
Fix copyright dates and add new functions to wand_symbols.h
Fix corrupted PNG output when matte channel is enabled with no transparent pixels.
GIF: Log when Netscape loop extension iterations are read or written.
Added Magick++ Image::thumbnail() method for fast resize.
Support use of clang/llvm __attribute__ and __builtin extensions similar to the existing support for GCC.
Support compiling for "pure" OpenMP environment.
PAM fix for scaling of alpha in sub-ranged pixels.
Remove accidential print to stdout in Wand MagickDrawImage()
Added Wand API functions MagickGetImageGeometry, MagickSetImageGeometry, MagickGetImageMatte, and MagickSetImageMatte.
Use existing image resolution when writing PDF.
Postscript writers should be resolution from image similar to PDF.