calculate_exclude_regexp (Rake::FileList)

          # File lib/rake.rb, line 1123
    1123:     def calculate_exclude_regexp
    1124:       ignores = []
    1125:       @exclude_patterns.each do |pat|
    1126:         case pat
    1127:         when Regexp
    1128:           ignores << pat
    1129:         when /[*.]/
    1130:           Dir[pat].each do |p| ignores << p end
    1131:         else
    1132:           ignores << Regexp.quote(pat)
    1133:         end
    1134:       end
    1135:       if ignores.empty?
    1136:         @exclude_re = /^$/
    1137:       else
    1138:         re_str = ignores.collect { |p| "(" + p.to_s + ")" }.join("|")
    1139:         @exclude_re = Regexp.new(re_str)
    1140:       end
    1141:     end