Use memory_info instead of memory_info_ex. Use memory_full_info with USS and PSS for the top process (extended stat) (related to issue#797)

Update all affected imports accordingly.

The psutil_version instance variable was erroneously declared as private
(using name mangling).

This way we avoid leaving sockets open which can trigger a
ResourceWarning in some cases.

Fix bug introduced in commit e350cb5b.

See https://github.com/nicolargo/glances/issues/546#issuecomment-175272479

This reverts commit eee6dd6d, reversing
changes made to dbb97a53.

Fix #719

fix #740

Segmentation fault on OpenBSD too.
See commit 7cfc223c for more info.