(capital gain taxes incurred as result of post-confirmation of Chapter 12 plan for debtors' dairy operation remain a secured claim - 11 U.S.C. Sec. 1222(a)(2)(A) inapplicable to post-confirmation sale of farm assets; confirmed plan in place before any sale of farm assets contemplated and debtor cannot modify plan to change such result; court noted that Ninth Circuit decision in Hall adopted "plain meaning" approach to applying 11 U.S.C. Sec. 1222(a)(2)(A) and determined it to persuasively control the issue; court noted that Chapter 12 bankruptcy estate is not treated as a separate taxable entity from the debtor, thus "incurred by the estate" cannot mean "incurred post-petition"; while court not entirely persuaded by either Hall or Knudsen approach, court would side with Hall, but noted that this case involved post-confirmation sale rather than post-petition).