Added tree model process view.

This model builds a tree model out of a list model.
Sort the tree according to the list model.
Added the process tree to the settings.
add m4/
uninitialized variable in solaris backend
Repair memory and swap size calculation on OpenBSD.
Add a show-memory-in-xbytes checkbox and its corresponding property
Remove memory_human_size and use g_format_size instead
connect the notify::show-memory-in-xbytes signal to a force_timeout_update() call
Display the memory usage as bytes instead of a percentage when show-memory-in-xbytes is set (#6503)

- move the percentage calculation to init_timeout(), use g_format_size() here too
- carry memory/swap used vs total all around
- make the XtmProcessStatusbar swap and memory properties strings instead of float

Based on a diff from  Ján Sucan, thanks!

Note to translators: this changes some strings, mostly removing % in format printing
Merge branch 'peter/tree-model'