Numerous bug fixes and improvements

Dartmouth/setStewartCh18S1/problem_1a.pg  Fixed bug in which it would not accept answers in either order.
Rochester/setIntegrals25RationalFunctions/ur_in_25_22.pg Fixed typo in TeX mode, and some code cleanup.
Utah/Calculus_II/set5_Techniques_of_Integration/set5_pr10.pg Fixed broken link.
Utah/Calculus_II/set11_Conics_and_Polar_Coordinates/set11_pr2.pg Fixed typos and some code cleanup.
UMN/calculusStewartCCC/s_3_2_10.pg Made answer blank longer (random seed 4720, for example).
Utah/AP_Calculus_I/set7_Trigonometric_Functions/1210s4p17.pg Made answer blank longer.
Utah/AP_Calculus_I/set12_Further_Techniques_and_Applications_of_Integration/1220s14p4.pg Some clarifications, and made solution agree with correct answer.
Dartmouth/setStewartCh12S2/problem_12.pg Recognized that the formula is only for n>1.
Union/setIntByParts/sc5_6_07.pg Fixed "Could not generate enough valid points" with random seed 216.
Rochester/setSeries6CompTests/ur_sr_6_16.pg Fixed wrong answer with random seed 63.
maCalcDB/setDiffEQ5ModelingWith1stOrder/ur_de_5_2.pg Made instructions agree with required answer.
Rochester/setDiffEQ5ModelingWith1stOrder/ur_de_5_17.pg Added more details in the problem statement, and added keyword 'separated'.
FortLewis/DiffEq/1-First-order/04-Linear-integrating-factor/integrating-factor-02.pg Added clarifying comment "Enter your answer as y=..."
FortLewis/DiffEq/1-First-order/04-Linear-integrating-factor/KJ-2-2-22.pg Same as above.
FortLewis/DiffEq/2-Higher-order/02-Linear-2nd-order-cc/Lebl-2-2-06.pg Same
FortLewis/DiffEq/2-Higher-order/02-Linear-2nd-order-cc/Lebl-2-2-08.pg Same
UMN/calculusStewartET/s_9_3_1.pg Erroneously rejected correct answer C|x|^5.
Utah/AP_Calculus_I/set5_The_Integral/sc5_4_19a.pg Changed the integrand to one that is not as easy to evaluate directly.