improve the gridpts algorithm to ignore obvious duplicates

[mmckerns]

improve the gridpts algorithm to ignore obvious duplicates

For example, repeat points occur (so should ignore) when:

• nbins[:] = 1
• upper[:] = lower[:]

[mmckerns]

Code should go something like this:

bins.append( newbin )

# Hence, we have, for example:  bins = [[ A1, B1, C1], [A1, B1, C1], [A2, B1, C1], ...]

# ... and we filter for existing bins
rbins = [bin[:-1] for bin in bins]
if newbin[:-1] not in rbins:
  bin.append( newbin )