Fix implicit function declaration

--- a/src/xml2ps.c
+++ b/src/xml2ps.c
@@ -36,7 +36,7 @@
 void read_sugar_syn(char *inpfile, long **sugar_syn);
 void get_sugar_syn(FILE *inp, char *value_ch);
 void get_chain_broken(long nres, double **a, double **b, long *chain_broken);
-
+extern void get_BDIR(char *BDIR, char *filename);
 
 
 FILE  *psfile;