ARM-specific optimization processes 8 or 4 pixels at once.
Improves performance by around 10-22% on a recent ARM Chromebook.

Also added one msa optimized function: png_read_filter_row_up_msa
Signed-off-by: NMandar Sahastrabuddhe <Mandar.Sahastrabuddhe@imgtec.com>

Moved it from bin_PROGRAMS to check_PROGRAMS in Makefile.am so it will be
built but not installed.

This adds pngcp to the build together with a pngcp.dfa configuration test; the
test revealed some configuration bugs which are fixed by corrections to the
_SUPPORTED macros.

pngcp builds on all tested configurations and a number of bugs have been fixed
to make this happen relative to the version in libpng 1.7 contrib/examples.
pngcp.dfa will have to be different for 1.7 but pngcp.c should work fine (not
yet tested).  pngcp itself is still missing a usage message; this is a
preliminary version, although since it behaves the same way as 'cp' most unoids
shouldn't have a problem using it correctly.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

presence of clock_gettime() in configure.ac and Makefile.am.

on platforms that don't supply clock_gettime().

inadvertently replaced with libpng17 versions).

Signed-off-by: NJohn Bowler <jbowler@acm.org>

tests/pngstest-* are changed so that the new test files are divided into 8
groups by gamma and alpha channel.  This makes each test take just under 5
seconds on a moderately up-to-date x86_64 system using libpng16 (test times are
somewhat variable under libpng17 at present because of the lack of optimization
in some gamma processing paths.)

These tests have considerably better code and pixel-value coverage than
contrib/pngsuite however coverage is still incomplete.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

pnglibconf.* in "make clean" (Cosmin).