Declare pg_encoding_to_char() to avoid an implicit declaration (by Aurélien
GÉRÔME <ag@roxor.cx>).

diff -urNad ruby-pg-0.7.9.2008.03.18~/ext/pg.c ruby-pg-0.7.9.2008.03.18/ext/pg.c
--- ruby-pg-0.7.9.2008.03.18~/ext/pg.c	2006-10-16 01:38:23.000000000 +0200
+++ ruby-pg-0.7.9.2008.03.18/ext/pg.c	2006-10-16 01:38:38.000000000 +0200
@@ -25,6 +25,8 @@
 
 #define rb_define_singleton_alias(klass,new,old) rb_define_alias(rb_singleton_class(klass),new,old)
 
+extern const char *pg_encoding_to_char(int encoding); /* Taken from mb/pg_wchar.h. */
+
 static VALUE rb_cPGconn;
 static VALUE rb_cPGresult;