[PATCH] Add cpu_affinity_map configuration option to bind workers to cores

Add cpu_affinity_map configuration option to bind workers to CPU cores.

Allows the admin to place all workers on individual cores without
writing a lot of if-statements. For example,

     cpu_affinity_map process_numbers=1,2,3,4 cores=1,3,5,7

will have an effect for kids 1 through 4 only and will place them on
even cores starting with core #1.

If there are conflicts for a given process, the latest option wins and
a warning is printed. If the number of specified processes do not match
the number of specified cores, Squid quits with an error. Multiple
cpu_affinity_map options are merged.

Squid builds on systems without Linux CPU affinity calls, but setting
affinity only works if there are sched_getaffinity(2) and
sched_setaffinity(2) available. If there is no OS support but
cpu_affinity options are configured, Squid quits with an error. If there
is OS support but calls fail, Squid prints an error but does not quit.