This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
-K: set keepalive SLIP timeout
-O: set outfill SLIP timeout
Handle SIGURG from keepalive like SIGHUP now, i.e. reconnect.
Back out background scription change, cause some synchro problems.
Now works with dialin devices too.
Add new option in slattach style -l: dont use modem control.
Add new option -W: specify max number of dial tries for one phone.
Remove -p option, this ugly hack not needed.
Fix script timeout expires.
Some code cleanups.
Add -t to specify login script timeout.
Add -w to specify retry wait time.
Describe -p option.
Now understand several -s sections (for several host phone numbers).
Remove -F sw (software flow control), it is impossible with slip.
Change -F hw (hardware flow control) option to -h as in slattach,
we don't need option with argument for only one case.
Call downscript on SIGTERM.
Improve debug diagnostic.
Allow startslip work with several slip lines without killing each other.
Unlink pid file on exit.
Skip \r and \0 in login script parsing instead making them \n.
Use absolute path to default script (/sbin/ifconfig).
Call up/down script in background to prevent hang on them.
