safehasattr: pass attribute name as string instead of bytes
This is a step toward replacing `util.safehasattr` usage with plain `hasattr`.
The builtin function behave poorly in Python2 but this was fixed in Python3.
These change are done one by one as they tend to have a small odd to trigger
puzzling breackage.
local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed