removing unused variable cache_stat

Signed-off-by: Petr Holasek <pholasek@redhat.com>
Manpage note about ignoring of --pid in some cases

Signed-off-by: Petr Holasek <pholasek@redhat.com>
irqbalance signal handling tuning

Added sigaction for SIGTERM, SIGUSR1 and SIGUSR2 using the same handler
like SIGINT, i.e. stop and cleanup after finishing of current balancing
iteration.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
Warning when irqbalance hasn't root privileges

Signed-off-by: Petr Holasek <pholasek@redhat.com>