Renaming

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24646 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] incomplete_lower_gamma -> igamma

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24647 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e