Fixing Diff algo once again

Will filter out outliers beginning at block 5800
Fixed PID calculating wrong Diff

Doh!
Added new checkpoints
Fixed PID checkpointing
Fixed PID checkpointing part deux
Added new checkpoint at block 5860

Just in case
Give the checkpoint more time.
Allow extra 24 hours for checkpoints

Really annoyed by the 'block with timestamp before last checkpoint'
error
Fixed compiler warning

signed and unsigned integer comparison
Damn checkpoint timestamp

Set it back to the genesis block date
Fixed the InitPIDstate function

To cover all the cases.
New Branch 0.3.8
Prevent zero values to be fed into the PID

They have the potential of increasing the Diff too fast.  Will use
TxTime for average instead
One more fix for the PID Init
There was another fork at 5900

Thanks the Diff algo
One more change to PID Init