pkg/uid: fix integer overflow on 32-bit systems
pkg/uid: fix integer overflow on 32-bit systems

Since integer constants on 32-bit platforms are signed 4-byte integers, some of
them overflow. They therefore need explicit casting.

coreos/rkt,jjlakis/rkt,lucasallan/rkt,liugenping/rkt,akshaykarle/rkt,jzelinskie/rkt,sgotti/rkt,tmrts/rkt,lucasallan/rkt,coreos/rkt,cab105/rkt,s-urbaniak/rkt,cab105/rkt,coreos/rkt,jjlakis/rkt,matthaias/rkt,achanda/rkt,matthaias/rkt,squeed/rkt,jasonchaffee/rkt,monstermunchkin/rkt,dgonyeo/rkt,rkt/rkt,kbrwn/rkt,akshaykarle/rkt,euank/rkt,sinfomicien/rkt,sgotti/rkt,blixtra/rkt,joshix/rkt,yifan-gu/rkt,il9ue/rkt,alban/rkt,yifan-gu/rocket,sinfomicien/rkt,endocode/rkt,dgonyeo/rkt,mike1729/rkt,linki/rkt,tmrts/rkt,ybubnov/rkt,joshix/rkt,euank/rkt,Shashwatsh/rkt,Shashwatsh/rkt,il9ue/rkt,endocode/rkt,krnowak/rkt,markllama/rkt,kinvolk/rkt,joshix/rkt,monstermunchkin/rkt,shobhit85/rkt,alban/rkt,jasonchaffee/rkt,markllama/rkt,endocode/rkt,kinvolk/rkt,jakon89/rkt,achanda/rkt,blixtra/rkt,jonboulle/rkt,s-urbaniak/rkt,shobhit85/rkt,yifan-gu/rocket,alban/rkt,jonboulle/rkt,blixtra/rkt,cab105/rkt,jzelinskie/rkt,yifan-gu/rkt,yifan-gu/rkt,kinvolk/rkt,intelsdi-x/rkt,s-urbaniak/rkt,nhlfr/rkt,liugenping/rkt,il9ue/rkt,euank/rkt,monstermunchkin/rkt,linki/rkt,jonboulle/rkt,jakon89/rkt,matthaias/rkt,sinfomicien/rkt,Shashwatsh/rkt,krnowak/rkt,jasonchaffee/rkt,kbrwn/rkt,kinvolk/rkt,jzelinskie/rkt,squeed/rkt,lucasallan/rkt,akshaykarle/rkt,rkt/rkt,dgonyeo/rkt,squeed/rkt,nhlfr/rkt,Wilybald/rkt,lucasallan/rkt,markllama/rkt,mike1729/rkt,shobhit85/rkt,achanda/rkt,jakon89/rkt,sstabellini/rkt,Wilybald/rkt,jjlakis/rkt,liugenping/rkt,intelsdi-x/rkt,mike1729/rkt,tmrts/rkt,joshix/rkt,Wilybald/rkt,ybubnov/rkt,sstabellini/rkt,sstabellini/rkt,rkt/rkt,sgotti/rkt,Wilybald/rkt,rkt/rkt,kbrwn/rkt,intelsdi-x/rkt,krnowak/rkt,nhlfr/rkt,yifan-gu/rocket,linki/rkt,ybubnov/rkt