Bib:fix tm-alpha style when bibtex file has comments

git-svn-id: svn://svn.savannah.gnu.org/texmacs/trunk@8813 64cb5145-927a-446d-8aed-2fb7b4773692
Extra example


git-svn-id: svn://svn.savannah.gnu.org/texmacs/trunk@8814 64cb5145-927a-446d-8aed-2fb7b4773692