[giac] remove all exact() wrapping (not needed now that all numbers are sent to giac as fractions)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24908 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] exact() put back in Rationalize.1 (still needed for eg Rationalize[1/(ί+1)] )

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24909 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] updated unit tests

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24910 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e