Merge branch 'cb/avoid-colliding-with-netbsd-hmac'

The <stdlib.h> header on NetBSD brings in its own definition of hmac() function (eek), which conflicts with our own and unrelated function with the same name. Our function has been renamed to work around the issue. * cb/avoid-colliding-with-netbsd-hmac: builtin/receive-pack: avoid generic function name hmac()