+/**
+ * Search a TeX file in all locations the latex compiler would search it,
+ * with the help of kpsewhich.
+ * The current working directory must be set correctly, so that relative
+ * names work.
+ * \param fil The filename to search
+ * \param format The file format as used by kpsewhich, e.g. "bib", "bst" etc.
+ */