Add function to return the thread safety status of libpq

This is half of an item in TODO list. I patch this because now pgbench is
threaded in Win32, so it is better to check thread safety of libpq.dll.

Patch ecpg could be done in a similar way, but I am not sure how we will
use this function there ...

Regards,
Qingqing

---

Index: fe-connect.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/interfaces/libpq/fe-connect.c,v
retrieving revision 1.324
diff -c -r1.324 fe-connect.c
*** fe-connect.c	22 Nov 2005 18:17:32 -0000	1.324
--- fe-connect.c	3 Dec 2005 05:15:29 -0000
***************
*** 2860,2865 ****
--- 2860,2875 ----
  	return PG_PROTOCOL_MAJOR(conn->pversion);
  }

+ bool
+ PQthreadSafe(void)
+ {
+ #ifdef ENABLE_THREAD_SAFETY
+ 	return true;
+ #else
+ 	return false;
+ #endif
+ }
+
  int
  PQserverVersion(const PGconn *conn)
  {
Index: libpq-fe.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/interfaces/libpq/libpq-fe.h,v
retrieving revision 1.122
diff -c -r1.122 libpq-fe.h
*** libpq-fe.h	23 Nov 2005 04:23:28 -0000	1.122
--- libpq-fe.h	3 Dec 2005 05:15:29 -0000
***************
*** 264,269 ****
--- 264,270 ----
  extern const char *PQparameterStatus(const PGconn *conn,
  				  const char *paramName);
  extern int	PQprotocolVersion(const PGconn *conn);
+ extern bool	PQthreadSafe(void);
  extern int	PQserverVersion(const PGconn *conn);
  extern char *PQerrorMessage(const PGconn *conn);
  extern int	PQsocket(const PGconn *conn);