dmesg(1) changes for util-linux 2.20

I have re-written the dmesg(1). That's the first large change in the code in last 18 years.

New features:

• --decode facility and level number to human readable prefixes

$ dmesg --decode
kern  :info  : [26443.677632] ata1.00: configured for UDMA/100
kern  :info  : [26443.830225] PM: resume of devices complete after 2452.856 msecs
kern  :debug : [26443.830606] PM: Finishing wakeup.
kern  :warn  : [26443.830608] Restarting tasks ... done.

• filter out messages according to the --facility and --level options, for example

$ dmesg --level=err,warn

$ dmesg --facility=daemon,user

$ dmesg --facility=daemon --level=debug

• -u, --userspace to print only userspace messages


• -k, --kernel to print only kernel messages


• -t, --notime to skip [...] timestamps


• -T, --ctime to print human readable timestamp in ctime()-like format. Unfortunately, this is useless on laptops if you have used suspend/resume. (The kernel does not use the standard system time as a source for printk() and it's not updated after resume.)


• --show-delta to print time delta between printed messages
  

$ dmesg --show-delta
[35523.876281 <    4.016887>] usb 1-4.1: new low speed USB device using  hci_hcd and address 12
[35523.968398 <    0.092117>] usb 1-4.1: New USB device found, idVendor=413c, idProduct=2003
[35523.968408 <    0.000010>] usb 1-4.1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[35523.968416 <    0.000008>] usb 1-4.1: Product: Dell USB Keyboard