Support rotate=N option on access_log

Support rotate=N option on access_log

Add a rotate=N option to access_log directive to set per-log what the
retained log count will be. At present it is only used by the stdio:
logging module, which is also the only one to use logfile_rotate
directive.

If this option is absent (as will be the common case) the log rotation
defaults to using the value of logfile_rotate directive.

Also, add missing dump output of other access_log options if they differ
from the defaults.

The use-cases for this are:

1) Unix fifo logging requires all the stdio: module operations except
that the normal rotate/rename operation is NOT performed on the fifo
socket. It makes more sense to add this option which can also meet case
#2 than to create a whole new module just for fifo.

2) managing only some access_log files with a third-party log manager.
Those specific logs need rotate=0, but the Squid managed logs may
require non-0 values.