(taxpayers, married couple, donated qualified conservation easement to qualified organization and received state income tax credits in return; pursuant to state law, taxpayers later gave away $10,000 in credits and sold $110,000 credits (net return of $82,500 computed with basis in credits of $4,897); based on I.R.C. Sec. 1221, court held that credits are capital in nature, noting that taxpayers not eligible for refund on sale of credits; credits never part of taxpayers' property rights and were short-term capital assets; I.R.C. Sec. 170 does not allow basis allocation in proportion to credit value, so taxpayers had no income tax basis in credits).