Show an appropriate error message when the command line --append flag fails to open...
tree926a8a84601418e91b4818adcff8e4da589d4f35
-rw-r--r-- 3741 .gitignore
-rw-r--r-- 1453 .valgrind
drwxr-xr-x - ETL
drwxr-xr-x - autobuild
drwxr-xr-x - gtkmm-osx
drwxr-xr-x - synfig-core
drwxr-xr-x - synfig-docs
drwxr-xr-x - synfig-osx
drwxr-xr-x - synfig-studio