gio-tool: Various fixes related to error messages

This patch contains the following changes:
- Print all errors with "gio: " prefix
- Print file uri in error for each tool allowing multiple locations
- Mark all error messages translatable
- Do not leak strings used in error messages
- Always start error messages with capital letter
- Unify some error messages across various tools
- Fix addional/missing new line characters

https://bugzilla.gnome.org/show_bug.cgi?id=776169

gio/gio-tool.h

@@ -20,8 +20,11 @@
 #ifndef __GIO_TOOL_H__
 #define __GIO_TOOL_H__
 
+void print_error      (const gchar    *format,
+                       ...);
 void print_file_error (GFile          *file,
-                       const char     *message);
+                       const gchar    *format,
+                       ...);
 void show_help        (GOptionContext *context,
                        const char     *message);