Don't use deprecated isc_interprete() in Firebird backend.

Using isc_interprete() is unsafe because it doesn't take the buffer size and
results in deprecation warnings with Firebird 2.x. Use the new fb_interpret()
instead to fix both problems.

Notice that this breaks compilation with Firebird 1.x but hopefully this is
not a problem as it's pretty old by now.

Signed-off-by: Vadim Zeitlin <vz-soci@zeitlins.org>

src/backends/firebird/error-firebird.cpp

@@ -37,16 +37,16 @@ namespace firebird
 void get_iscerror_details(ISC_STATUS * status_vector, std::string &msg)
 {
     char msg_buffer[SOCI_FIREBIRD_ERRMSG];
-    ISC_STATUS *pvector = status_vector;
+    const ISC_STATUS *pvector = status_vector;
 
     try
     {
         // fetching first error message
-        isc_interprete(msg_buffer, &pvector);
+        fb_interpret(msg_buffer, SOCI_FIREBIRD_ERRMSG, &pvector);
         msg = msg_buffer;
 
         // fetching next errors
-        while (isc_interprete(msg_buffer, &pvector))
+        while (fb_interpret(msg_buffer, SOCI_FIREBIRD_ERRMSG, &pvector))
         {
             msg += "\n";
             msg += msg_buffer;