Omit htonll when already #defined
Omit htonll when already #defined

OS X 10.10 Yosemite defines it as a macro.

Signed-off-by: R. Andrew Ohana <0e3d4bf85c48fa098afd9746852f73da1fc0e45f@gmail.com>
[1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org: adjust comments; adjust commit message]
Reviewed-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>
Tested-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>

gevaerts/bup,tjanez/bup,mhoeher/bup,ToxicFrog/bup,pombredanne/bup,gevaerts/bup,jbaber/bup,gevaerts/bup,mhoeher/bup,pombredanne/bup,pombredanne/bup,pombredanne/bup,ToxicFrog/bup,mhoeher/bup,ToxicFrog/bup,tjanez/bup,jbaber/bup,tjanez/bup,tjanez/bup,gevaerts/bup,jbaber/bup,gevaerts/bup,pombredanne/bup,ToxicFrog/bup,pombredanne/bup,jbaber/bup,mhoeher/bup,mhoeher/bup,ToxicFrog/bup,tjanez/bup,jbaber/bup,mhoeher/bup,jbaber/bup,tjanez/bup