v1.6.19

Release was delayed because of a backlog of patches which I kept thinking I would have time to merge in, but it kept not happening. So this is a rollup of the various bug fixes and cleanups which have been waiting to be released for a while, instead of waiting forever.

• fix: starting pv in the background no longer immediately stops unless the transfer is to/from the terminal (Andriy Gapon, Jonathan Elchison)
• fix: using -B, -A, or -T now switches on -C implicitly (Johannes Gerer, André Stapf)
• fix: AIX build fixes (Peter Korsgaard)
• i18n: updated German "--help" translations (Richard Fonfara)
• i18n: switched to UTF-8 encoding, added missing translations (de,fr,pt)
• docs: new "common switches" manual section (Jacek Wielemborek)
• docs: use placeholder instead of /dev/sda in the manual (Pranav Peshwe)
• docs: mention MacOS pipes and "-B 1024" in the manual (Jan Venekamp)
• docs: correct shell in autoconf/scripts/index.sh (Juan Picca)
• cleanup: various compiler warnings cleaned up