[MixMaster] Display more useful error messages

Include the full text of the original exception, and print this to the terminal
as well.

interfaces/cython/cantera/mixmaster/Edit.py

@@ -179,8 +179,8 @@ class EditFrame(Frame):
         try:
             self.redraw()
             self.app.makeWindows()
-        except:
-            handleError('Edit err')
+        except Exception as e:
+            handleError('Edit err:\n'+str(e))
 
         self.app.mix = IdealGasMixture(self.app.mech)
         self.mix = self.app.mix

interfaces/cython/cantera/mixmaster/main.py

@@ -68,9 +68,9 @@ class MixMaster:
             self.mech = Solution(pathname)
             self.mechname = ff[0]
 
-        except:
+        except Exception as e:
             utilities.handleError('could not create gas mixture object: '
-                                  +ff[0]+'\n')
+                                  +ff[0]+'\n'+str(e))
             self.mechname = 'Error'
             return
 

interfaces/cython/cantera/mixmaster/utilities.py

@@ -28,6 +28,9 @@ def _print_value(name, value, unitstr):
 
 def handleError(message = '<error>', window = None,
                 fatal = 0, warning = 0, options = None):
+    # Print the message to the terminal, since this can at least be copied and
+    # pasted, unlike the contents of the dialog box.
+    print(message)
     if warning:
         messagebox.showwarning(title = 'Warning', message = message,
                                parent = window)