fix mknod and mknodat to accept large dev_t values

support for these was recently added to sysmacros.h. note that the
syscall argument is a long, despite dev_t being 64-bit, so on 32-bit
archs the high bits will be lost. it appears the high bits are just
glibc silliness and not part of the kernel api, anyway, but it's nice
that we have them there for future expansion if needed.

global cleanup to use the new syscall interface

initial check-in, version 0.5.0