Add *.opendb and *.idb to .gitignore
Add *.opendb and *.idb to .gitignore

.opendb is a new kind of cache added in VS2015 Update 1.
.idb is produced by VC compiler.

gregkalapos/corert,manu-silicon/corert,sandreenko/corert,mjp41/corert,shrah/corert,mjp41/corert,manu-silicon/corert,schellap/corert,sandreenko/corert,kyulee1/corert,krytarowski/corert,manu-silicon/corert,manu-silicon/corert,shrah/corert,shrah/corert,schellap/corert,kyulee1/corert,mjp41/corert,gregkalapos/corert,manu-silicon/corert,yizhang82/corert,mjp41/corert,gregkalapos/corert,botaberg/corert,gregkalapos/corert,krytarowski/corert,mjp41/corert,yizhang82/corert,botaberg/corert,schellap/corert,shrah/corert,sandreenko/corert,kyulee1/corert,yizhang82/corert,tijoytom/corert,botaberg/corert,schellap/corert,tijoytom/corert,krytarowski/corert,tijoytom/corert,botaberg/corert,tijoytom/corert,krytarowski/corert,kyulee1/corert,yizhang82/corert,schellap/corert,sandreenko/corert