didEnterResponderChain behaviours
This fixes the following bug: when editing the number of significant
digits, input "1+", click on "OK", the data was reloaded and "1+"
disappeared...
When each Calculation had its own text buffer, the Expression of an
overflowing output text was Undefined. Hence that Expression could have
been Undefined without the corresponding text being 'undef'. That situation
may not happen anymore since Calculation are stored in a shared buffer.
The most common case where only the approximate output is displayed
happens when the exact and the approximate outputs are equal, more
precisely when the exact output is equal to the approximate output with
the number of significant digits taken from user settings. That
clarification matters for the Poincare::Integers which have more digits than
the number of significant digits set by the user.
Besides, an Expression containing Units is simplified as
Multiplication(Float, Unit...) recorded identically into the exact and
the approximate outputs (except perhaps the number of significant
digits). Generally, the case where the number of digits in the output is
smaller or equal to the user setting would be matched by the condition,
stated above, that exact and approximate output are equal. But that
should also be the case whatever the number of significant digits. That
is why the presence of Units is matched specifically.
Solve an equation that has solutions, select a solution, then go back
and change the equation. WHen you go to the solutions, the previous
solution is still selected, which is a little weird
Scenario
Create an empty f function
Create g(x) = 1/x
Go to the graph
Change f(x) to f(theta) = theta^2 + 3
Go back to the graph -> the axes computation was very long
and 2 approximate outputs - one with the maximal number of significant
digits and one with the number of significant digits asked by the user.
This enables to find the approximate output without going through the
approximation routine again.
only when the calculation is actually expanded (when the output is
selected and the display output is ExactApproximateToggle)
This avoid blinking when changing input/output selection
AbstractScrollableExactApproximateExpressionsView children classes
reload scroll after reloading the subview selection when entering the
responder chain and when cell becomes first responder. We don't reload
scroll when setting content of cells as this is done every time we
relayout - when scrolling in the table for instance.
