Bug fixes, mostly adding "+C" and adding helpLinks for interval notation

Utah/Calculus_II/set15_Practice/sc5_5_8.pg  added +C
Rochester/setIntegrals25RationalFunctions/ur_in_25_11.pg  added +C
UVA-Stew5e/setUVA-Stew5e-C05S05-Substitution/5-5-40.pg  added +C and "etc."
Rochester/setIntegrals25RationalFunctions/ur_in_25_12B.pg  "+C" --> "+K" (C is used in partial fractions)
Utah/Calculus_II/set4_Techniques_of_Integration/set4_pr11.pg  added +C; removed confusing "+c" from expected answer
WHFreeman/Rogawski.../8.1.13.pg  fixed subtle perl error "Use of uninitialized value $str"
UMN/calculusStewartCCC/s_1_3_36.pg  added helpLinks for interval notation
UMN/calculusStewartCCC/s_11_2_41.pg  same
UMN/calculusStewartCCC/s_11_2_44.pg  same