OpenSystemsDevelopment / qpdf

Lazily load MD5 and RC4 once in the life of the program. Only load the
legacy provider if RC4 is actually being used.

Add comments to force line breaks, parenthesize function arguments
that are contatenated strings, etc. -- these kinds of changes improve
clang-format's results and also cause emacs cc-mode to match
clang-format. After this type of change, most of the time, when
clang-format and emacs disagree, clang-format is better.

Run this:

for i in  **/*.cc **/*.c **/*.h **/*.hh; do
  clang-format < $i >| $i.new && mv $i.new $i
done

Fixes qpdf/qpdf#450

Fixes qpdf/qpdf#417