MEDIUM: cfgparse: post parsing registration

Allow to register a function which will be called after the
configuration file parsing, at the end of the check_config_validity().

It's useful fo checking dependencies between sections or for resolving
keywords, pointers or values.
diff --git a/include/common/cfgparse.h b/include/common/cfgparse.h
index fc96bfe..230c35f 100644
--- a/include/common/cfgparse.h
+++ b/include/common/cfgparse.h
@@ -75,6 +75,7 @@
 int cfg_register_section(char *section_name,
                          int (*section_parser)(const char *, int, char **, int),
                          int (*post_section_parser)());
+int cfg_register_postparser(char *name, int (*func)());
 void cfg_unregister_sections(void);
 void cfg_backup_sections(struct list *backup_sections);
 void cfg_restore_sections(struct list *backup_sections);