Default refresh to True (ebuild)

See #3302
Make both "refresh=true" and "refresh=True" work

Also pep8 fixes.
Default refresh to True (pkgutil) + pep8 fixes

See #3302
Add refresh param + pep8 fixes

list_upgrades and upgrade are not yet implemented, but I added some
commented-out bits that can be uncommented once these functions are
implemented.
Default refresh to True (yumpkg) + pep8 fixes

See #3302
Default refresh to True (yumpkg5) + pep8 fixes

See #3302
Default refresh to True (zypper) + pep8 fixes

See #3302
Prevent traceback using refresh param

This commit forces the 'refresh' param to be cast as a string to keep
things like 'refresh: 123' in a pkg state from causing a TypeError.
Prevent traceback using refresh param

Make the same change as was made in f0d1043 to pacman.py
Fix typo introduced in f0d1043
Merge pull request #3311 from archtaku/list_upgrades

Make pkg.list_upgrades, pkg.upgrade default to refresh=True