OpenSystemsDevelopment / qpdf

Run this:

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

Use get() and use_count() instead. Add #define
NO_POINTERHOLDER_DEPRECATION to remove deprecation markers for these
only.

This commit also removes all deprecated PointerHolder API calls from
qpdf's code except in PointerHolder's test suite, which must continue
to test the deprecated APIs.

Preparing to refactor some pattern searching code to use these instead
of their own memchr loops. This should simplify the code that replaces
PCRE.