fix test suite thresholds

changes in jpg encode/decode mean we must adjust test suite thresholds

Merge branch '8.5'

better nlines calc

better cache sizing for some image widths

Merge branch 'add-markdown-docs' into 8.5

supps for helgrind

fix --without-libexif

there was an ExifData missing a #ifdef guard in jpeg.h

as uploaded

as uploaded

as 8.2.2 tarball

version 8.2.3