Possible move of comparison to a separate function inside set

[dmadeka]

try:
   silent = bool(old_value == new_value)
except:
   # if there is an error in comparing, default to notify
   silent = False

When == doesn't work (think np.array or pd.DataFrame), this is equivalent to failing silently in some sense. We should move this section to a separate compare function that can be overload by a TraitType so the entire logic of set doesn't need to be copied.

[dmadeka]

Just saw #276