- (djm) [configure.ac] We now require a working vsnprintf everywhere (not
   just for systems that lack asprintf); check for it always and extend
   test to catch more brokenness. Fixes builds on Solaris <= 9
 - (djm) [sftp-server.c] Some systems (e.g. Irix) have prctl() but not
   PR_SET_DUMPABLE, so adjust ifdef; reported by Tom Christensen