[patch] Add physical units support for comedilib demo programs

The attached patch adds a "-p" option to common.c that programs can use 
to decide whether to output raw values or physical values.  The patch 
also includes modifications to the cmd and inp programs to use this 
flag.  Here is what the output looks like without -p and with -p...

$ ./cmd -f /dev/comedi1 -s 0 -r 1 -g -c 16 -n 5 -N 4 2>/dev/null
50959 48145 49835 49755 50823
50961 48146 49838 49757 50821
50957 48147 49837 49749 50823
50961 48143 49833 49754 50823

$ ./cmd -f /dev/comedi1 -s 0 -r 1 -g -c 16 -n 5 -N 4 -p 2>/dev/null
2.77676 2.34615 2.60494 2.59182 2.75494
2.77661 2.34585 2.60464 2.59289 2.75433
2.77646 2.3463  2.60418 2.59197 2.75555
2.77646 2.34585 2.60388 2.59319 2.75525

$ ./inp -f /dev/comedi1 -s 0 -r 1 -g -c 16
50960

$ inp -f /dev/comedi1 -s 0 -r 1 -g -c 16 -p
2.77523 V

$ inp -f /dev/comedi1 -s 0 -r 1 -g -c 16 -v
measuring device=/dev/comedi1 subdevice=0 channel=16 range=1 analog 
reference=0
50957

$ inp -f /dev/comedi1 -s 0 -r 1 -g -c 16 -p -v
measuring device=/dev/comedi1 subdevice=0 channel=16 range=1 analog 
reference=0
[0,65535] -> [-5,5]
2.77554 V (50957 raw units)

FWIW, the patch also sets OOR behavior to OOR_NUMBER for cmd and OOR_NAN 
for inp...

$ inp -f /dev/comedi1 -s 0 -r 4 -g -c 16 -p
Out of range [-0.5,0.5]

$ cmd -f /dev/comedi1 -s 0 -r 4 -g -c 16 -n 5 -N 4 -p 2>/dev/null
0.5     0.5     0.5     0.5     0.5
0.5     0.5     0.5     0.5     0.5
0.5     0.5     0.5     0.5     0.5
0.5     0.5     0.5     0.5     0.5


I chose OOR_NUMBER for cmd to make it easier to import the data dump 
into other programs (e.g. octave).  You'll also notice that I used a tab 
instead of a space as the delimiter in cmd's physical output (raw output 
remains unchanged).  It lines things up more neatly, but I don't really 
care whether it's a space or tab.  Might also want to include a '+' in 
the format specifier to line up + and - values better.

Dave