calculate_exclude_regexp (Rake::FileList)

          # File lib/rake.rb, line 1412
    1412:     def calculate_exclude_regexp
    1413:       ignores = []
    1414:       @exclude_patterns.each do |pat|
    1415:         case pat
    1416:         when Regexp
    1417:           ignores << pat
    1418:         when /[*?]/
    1419:           Dir[pat].each do |p| ignores << p end
    1420:         else
    1421:           ignores << Regexp.quote(pat)
    1422:         end
    1423:       end
    1424:       if ignores.empty?
    1425:         @exclude_re = /^$/
    1426:       else
    1427:         re_str = ignores.collect { |p| "(" + p.to_s + ")" }.join("|")
    1428:         @exclude_re = Regexp.new(re_str)
    1429:       end
    1430:     end