Applies the clang-format style to the 2.1 branch as done for master in 5dbf1809c6.
5dbf1809c6
They are not particularly packaged in Linux distros so we do not facilitate unbundling via SCons. There could be done if/when there is interest. Also s/pnm/pbm/, long-lived typo :) (cherry picked from commit b1e8889d96)
b1e8889d96