Principals bug in student.rb, Gets all grade specific principals in district

I should also refactor all_students_in_school as it doesn't really need an argument for the school.

Note in the code here, the second principals << line (156) does not filter by the specific school at all.

148 def special_group_principals
149 grades = enrollments.collect(&:grade)
150 schools = enrollments.collect(&:school_id)
151 principals = []
152
153 principals << district.special_user_groups.principal.all_students_in_district.collect(&:user)
154 schools.each do |school|
155 principals << district.special_user_groups.principal.all_students_in_school(school).collect(&:user)
156 principals << district.special_user_groups.principal.find_all_by_grouptype_and_grade(SpecialUserGroup::ALL_STUDENTS_IN_SCHOOL, grades).collect(&:user)
157 end
158
159 principals
160 end