[giac] Fix for constants of integration in regroup + fix for poisson_cdf

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28275 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Changing giac.js to the latest version in web/kickstart.xml

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28276 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
correct mimetype for images called foo.bar.png

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28277 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e