[giac] bugfix: don't change 1030.3 into 1033

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25178 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] make sure exact(1.0*10^100) isn't sent to Giac

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25179 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] updated unit tests

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25180 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e