*Summary : Structure for storing each parameter value of every slave device
is implemented.Also Polling strategy is Modified.

*)Created a structure for storing the previous values of all parameters
for each slave device(SLAVE_VAL_LIST).The latest value of each param
for each slave will be stored here.The database updation will take place
only if the obtained value is different from the stored value.

*)Modified the polling strategy,so that each slave will be polled 3 times
initially.After this only active slaves will be polled regularly.Then
again,after 10 polling cycles,the inactive slaves will be polled
again(3 times) to see if they have become active.(This rechecking
happens approximately in 10 minutes).