Parse libpq's "keepalives" option more like other integer options.

Use pqParseIntParam (nee parse_int_param) instead of using strtol
directly.  This allows trailing whitespace, which the previous coding
didn't, and makes the spelling of the error message consistent with
other similar cases.

This seems to be an oversight in commit e7a221797, which introduced
parse_int_param.  That fixed places that were using atoi(), but missed
this place which was randomly using strtol() instead.

Ordinarily I'd consider this minor cleanup not worth back-patching.
However, it seems that ecpg assumes it can add trailing whitespace
to URL parameters, so that use of the keepalives option fails in
that context.  Perhaps that's worth improving as a separate matter.
In the meantime, back-patch this to all supported branches.

Yuto Sasaki (some further cleanup by me)

Discussion: https://postgr.es/m/TY2PR01MB36286A7B97B9A15793335D18C1772@TY2PR01MB3628.jpnprd01.prod.outlook.com

src/interfaces/libpq/fe-connect.c

@@ -426,6 +426,8 @@ static void pgpassfileWarning(PGconn *conn);
 static void default_threadlock(int acquire);
 static bool sslVerifyProtocolVersion(const char *version);
 static bool sslVerifyProtocolRange(const char *min, const char *max);
+static bool parse_int_param(const char *value, int *result, PGconn *conn,
+							const char *context);
 
 
 /* global variable because fe-auth.c needs to access it */
@@ -1784,14 +1786,14 @@ connectFailureMessage(PGconn *conn, int errorno)
 static int
 useKeepalives(PGconn *conn)
 {
-	char	   *ep;
 	int			val;
 
 	if (conn->keepalives == NULL)
 		return 1;
-	val = strtol(conn->keepalives, &ep, 10);
-	if (*ep)
+
+	if (!parse_int_param(conn->keepalives, &val, conn, "keepalives"))
 		return -1;
+
 	return val != 0 ? 1 : 0;
 }
 
@@ -2627,8 +2629,7 @@ keep_going:						/* We will come back to here until there is
 
 						if (usekeepalives < 0)
 						{
-							appendPQExpBufferStr(&conn->errorMessage,
-												 libpq_gettext("keepalives parameter must be an integer\n"));
+							/* error is already reported */
 							err = 1;
 						}
 						else if (usekeepalives == 0)