Adds a new method isChanged() for determining if a value was changed.
This is done in preparation for a more elaborated caching method that is
handled inside the abstract base class.
Change-Id: Ica15f77d96453d30edd3a117c7185c694ad3691e
SQLite has global indices, not per table one. When using the database
updater to create the `unitest_math` table, we would get an error
with a duplicate `math_inputhash` index which is created by the the
database installer.
This patch skips the testBasicCreateTable() test on sqlite.
Change-Id: I6da56d67d7af45f86cf6163cf73f5464505b43f3
adds two new phpUnitTests for the abstract MathRender class
and another one that test the basic database access.
Therefore the read and write methods have been made changed
from protected to public.
Change-Id: I77a8b0a4dfe7529b5521ead097ac7b518688ef70
