[giac] parse back giac functions properly (eg Beta, fPart, Gamma, Psi, lower_incomplete_gamma, Ei, Ci, Si)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24619 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] parse back giac functions properly (mistake in last commit)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@24620 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e