sys/swap.h should work in large file environment
While implementing #640 Jason discovered that sys/swap.h barfs when a consumer has -D_FILE_OFFSET_BITS=64.
This appears to be because the swapres and swapent structures, which are a fixed part of the swapctl(2) syscall interface, use off_t in their definition which becomes 64 bits in a large file (lfcompile(5)) environment. Just replacing them with off32_t for
#if !defined(_LP64) should keep them consistent.