On Linux kernels the size of the values exported for block
device bytes has used a 64 bit integer for quite some time
(2.6+ IIRC). Make the procfs value extraction use correct
types and change internal types used to rate convert these
counters (within the DiskIO Meter) 64 bit integers, where
appropriate.
RichString_writeFrom takes a top spot during performance analysis due to the
calls to mbstowcs() and iswprint().
Most of the time we know in advance that we are only going to print regular
ASCII characters.
If the current data is smaller than the previous one, either by a retrieve error
or a device removal or a original data wraparound, sanitize the value to zero.
Fixes: #299
