sqlite3: Change return type of column_double from "f" to "d".

ffi now works properly with double return type, so this function can
return the correct type.  Can confirm that sqlite3_column_double now
works correctly on 32-bit and 64-bit x86.

Author: dpgeorge

sqlite3/sqlite3.py

@@ -24,7 +24,7 @@
 sqlite3_column_type = sq3.func("i", "sqlite3_column_type", "pi")
 sqlite3_column_int = sq3.func("i", "sqlite3_column_int", "pi")
 # using "d" return type gives wrong results
-sqlite3_column_double = sq3.func("f", "sqlite3_column_double", "pi")
+sqlite3_column_double = sq3.func("d", "sqlite3_column_double", "pi")
 sqlite3_column_text = sq3.func("s", "sqlite3_column_text", "pi")
 #sqlite3_int64 sqlite3_last_insert_rowid(sqlite3*);
 # TODO: should return long int