add test for spending siafunds
add test for spending siafunds

ericflo/Sia,MrStrong/Sia,mnsl/Sia,MrStrong/Sia,mharkus/Sia,ChrisSchinnerl/Sia,mtlynch/Sia,rivine/rivine,Mingling94/Sia,rivine/rivine,johnathanhowell/Sia,mnsl/Sia,mtlynch/Sia,mharkus/Sia,ericflo/Sia,NebulousLabs/Sia,ChrisSchinnerl/Sia,NebulousLabs/Sia