Make compatible with Octaves new exception-based error handling. Retain compatibility with Octaves old error handling based on error_state. * src/error_helpers.[h,cc]: Added. * src/Makefile.in: Integrate error-helpers.[h,cc]. * src/config.h.in: Added. * configure.ac, src/config.h.in: Test presence of 'error_state' and presence of 'verror (octave_execution_exception&, const char *, va_list)'. * src/__pq_connect__.cc, src/command.cc, src/command.h, src/converters.cc, src/converters_arr_comp.cc, src/pq_connection.cc, src/pq_conninfo.cc, src/pq_exec.cc, src/pq_lo.cc, src/pq_update_types.cc: If necessary, include error-helpers.h, replace error() with c_verror(), set and check a different error indicator than error_state, use CHECK_ERROR or SET_ERR, explicitely check for errors instead of relying on Octave checking error_state when returning to the prompt.

--- a/main/database/src/pq_update_types.cc	Fri Feb 26 15:07:46 2016 +0000
+++ b/main/database/src/pq_update_types.cc	Sat Feb 27 11:11:04 2016 +0000
@@ -48,7 +48,8 @@
   const octave_pq_connection &oct_pq_conn =
     dynamic_cast<const octave_pq_connection&> (rep);
 
-  oct_pq_conn.get_rep ()->octave_pq_refresh_types ();
+  if (oct_pq_conn.get_rep ()->octave_pq_refresh_types ())
+    error ("%s failed", fname.c_str ());
 
   return retval;
 }