Add "other" memory counter

Add "other" memory counter

The current memory counters taken from proc/meminfo don't add up
taking the entire usable physical memory. There is always a little bit
of memory left out from the equation that doesn't sum up. In some
situations that can be actualyl quite significant. Now this "Other"
memory has its own counter and the total amount of height of the
memory graph stays constant over time.

Signed-off-by: Timo Kokkonen <timo.t.kokkonen@iki.fi>