Upcast uptime from syscall

On arm and i386 the uptime value is int32 rather than int64,
so upcast to satify the function return value.
Merge pull request #41 from bz2/upcast_uptime

Upcast uptime from syscall
jsonhttp: new package
Merge pull request #42 from rogpeppe/001-jsonhttp

jsonhttp: new package
jsonhttp: use correct errgo package
Merge pull request #43 from rogpeppe/002-fix-errgo-import

jsonhttp: use correct errgo package
update to use gopkg.in/errgo.v1
Merge pull request #44 from rogpeppe/003-errgo.v1

update to use gopkg.in/errgo.v1