rotatelogs: add -n number-of-files option to roate through a number
of fixed-name logfiles. 




don't truncate the very first file opened (unless the truncate flag is there too)

Submitted by: covener
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1492708 13f79535-47bb-0310-9956-ffa450edef68