Read every value of a property in Fbe.same? so a later time matches

[Thayorns]

Fbe.same? read a property with fact.public_send(k), which gives back only its first value, so the .flatten around it had nothing to do. When the query found a fact by a Time that sat in the second or a later value, same? rejected it, and Fbe.if_absent and Fbe.just_one went on to insert a duplicate.

It now reads fact[k.to_s], which is every value of the property, and checks the time against all of them. A time that is in none of the values is still refused.

There was no test file for same.rb, so this adds one, together with a test in test_if_absent.rb and one in test_just_one.rb that insert a fact with two times and make sure no second fact appears.

Closes #1240

[Thayorns]

@yegor256 take a look please, happy to clarify anything about the change.