Remove all multi-threading, since it didn't actually make pg_view faster (the cpu load jumped from 50 to 180 with multiple threads.
Remove duplicate line
Move /proc/pid/stat field definitions to the global enum.
Transition to multiprocess implementation:
- use a separate process to run disk-intensive operations.
- the code is still not very efficient (i.e. we perform the same
disk operations for all detected DB clusters, even if some of them
really reside on the same device. There are some known bugs related
to screen refresh.
Fix a stupid bug when caching the du, df results while the new ones are not there.
Fix the problem of not showing data path properly (has been broken since transition to custom du.
Cache results of df.

When multiple PG clusters are running
on the same device, run df for it only once.