Fix for unbounded frequency regulation

[davidshumway]

For: #4
This has worked thus far but has not been extensively tested. Actually, have not ran into the lower bound case yet (100). But this ought to do the trick.

[davidshumway]

For the past few months I set max frequency to 393.75 using this code and it was stable. That is, this has been stable thus far: [ $maxtemp -lt $TMIN ] && [ $freq'' != "393.75" ]

[kmitz]

I issued a slightly more user-friendly fix on the develop branch. If that's ok for you I'll merge it to master.

[davidshumway]

After some further testing.

When $freq is valid:
root@antMiner:~# freq=$(cgminer-api stats | grep frequency] | awk '{print $3}'); echo \"$freq\"
"131.25"
root@antMiner:~# if [ $freq'' == 131.25 ]; then echo 'a'; fi;
a
root@antMiner:~# if [ $freq == 131.25 ]; then echo 'a'; fi;
a
root@antMiner:~# if [ $freq -lt 131.25 ]; then echo 'a'; fi;
sh: 131.25: bad number
root@antMiner:~# if [ $freq -lt 100 ]; then echo 'a'; fi;
sh: 131.25: bad number
root@antMiner:~# if [ $freq'' -lt 131.25 ]; then echo 'a'; fi;
sh: 131.25: bad number
root@antMiner:~# if [ $freq'' -lt 100 ]; then echo 'a'; fi;
sh: 131.25: bad number
root@antMiner:~# if [ $freq'' == 131.25 ]; then echo 'a'; fi;
a
root@antMiner:~# if [ $freq'' == "131.25" ]; then echo 'a'; fi;
a
root@antMiner:~# x=131.25; if [ $freq'' == $x ]; then echo 'a'; fi;
a

When $freq is empty/invalid:
root@antMiner:~# freq=$(cgminer-api stats | grep XXfrequency] | awk '{print $3}'); echo \"$freq\"
""
root@antMiner:~# if [ $freq'' == "131.25" ]; then echo 'a'; fi;
root@antMiner:~# if [ $freq'' == 131.25 ]; then echo 'a'; fi;
root@antMiner:~# if [ $freq'' -lt "131.25" ]; then echo 'a'; fi;
sh: bad number
root@antMiner:~# if [ $freq'' -lt "100" ]; then echo 'a'; fi;
sh: bad number
root@antMiner:~# if [ $freq -lt 100 ]; then echo 'a'; fi;
sh: 100: unknown operand
root@antMiner:~# x=131.25; if [ $freq'' == $x ]; then echo 'a'; fi;

So... further testing probably is necessary before using lt, gt, le, ge, etc.
However, if [ $freq'' == 131.25 ]; looks stable, i.e. if [ $freq'' == $MIN_FREQ ];.