MWL#36: Add a mysqlbinlog option to change the used database.

Make sql_alloc() declaration "public" for a client context.
The reason is that sql_alloc() is used in definition of some common
purpose stuff (e.g. sql_list.*). To make this stuff available for a
client context we declare sql_alloc() as a "virtual function", i.e.
as a function that is already declared but must be defined in this
context (note that definition of sql_alloc() in thr_malloc.cc is
#ifndef'ed for MYSQL_CLIENT).
Also make sql_string.h repeatedly includable.

client/sql_string.cc

@@ -26,15 +26,6 @@
 #ifdef HAVE_FCONVERT
 #include <floatingpoint.h>
 #endif
-
-/*
-  The following extern declarations are ok as these are interface functions
-  required by the string function
-*/
-
-extern void sql_alloc(size_t size);
-extern void sql_element_free(void *ptr);
-
 #include "sql_string.h"
 
 /*****************************************************************************

sql/mysql_priv.h

@@ -92,12 +92,16 @@ extern MYSQL_PLUGIN_IMPORT const char *primary_key_name;
 #include "unireg.h"
 
 void init_sql_alloc(MEM_ROOT *root, uint block_size, uint pre_alloc_size);
+#endif // MYSQL_CLIENT
+
 void *sql_alloc(size_t);
 void *sql_calloc(size_t);
 char *sql_strdup(const char *str);
 char *sql_strmake(const char *str, size_t len);
 void *sql_memdup(const void * ptr, size_t size);
 void sql_element_free(void *ptr);
+
+#ifndef MYSQL_CLIENT
 char *sql_strmake_with_convert(const char *str, size_t arg_length,
 			       CHARSET_INFO *from_cs,
 			       size_t max_res_length,

sql/sql_string.cc

@@ -26,15 +26,6 @@
 #ifdef HAVE_FCONVERT
 #include <floatingpoint.h>
 #endif
-
-/*
-  The following extern declarations are ok as these are interface functions
-  required by the string function
-*/
-
-extern uchar* sql_alloc(unsigned size);
-extern void sql_element_free(void *ptr);
-
 #include "sql_string.h"
 
 /*****************************************************************************

sql/sql_string.h

+#ifndef MYSQL_SQL_STRING_H_INCLUDED
+#define MYSQL_SQL_STRING_H_INCLUDED
 /* Copyright (C) 2000 MySQL AB
 
    This program is free software; you can redistribute it and/or modify
@@ -394,3 +396,5 @@ static inline bool check_if_only_end_space(CHARSET_INFO *cs, char *str,
 {
   return str+ cs->cset->scan(cs, str, end, MY_SEQ_SPACES) == end;
 }
+
+#endif // MYSQL_SQL_STRING_H_INCLUDED

sql/thr_malloc.cc

@@ -59,11 +59,13 @@ void init_sql_alloc(MEM_ROOT *mem_root, uint block_size, uint pre_alloc)
 }
 
 
+#ifndef MYSQL_CLIENT
 void *sql_alloc(size_t Size)
 {
   MEM_ROOT *root= *my_pthread_getspecific_ptr(MEM_ROOT**,THR_MALLOC);
   return alloc_root(root,Size);
 }
+#endif
 
 
 void *sql_calloc(size_t size)