Per discussion on irc on 12 Nov 2014, it seems that we should encourage projects that want to use valgrind.h, memcheck.h, etc, to #include them from system headers and do feature checks in the "normal" (autoconfy?) ways. And discourage projects from actually copying the files. * document the manual (where, though?) * maybe change the text at the top of the files, so as to explain the new guidelines Reproducible: Always