MEDIUM: cfgparse: post section callback

This commit implements a post section callback. This callback will be
used at the end of a section parsing.

Every call to cfg_register_section must be modified to use the new
prototype:

    int cfg_register_section(char *section_name,
                             int (*section_parser)(const char *, int, char **, int),
                             int (*post_section_parser)());
diff --git a/include/common/cfgparse.h b/include/common/cfgparse.h
index fd04b14..fc96bfe 100644
--- a/include/common/cfgparse.h
+++ b/include/common/cfgparse.h
@@ -73,7 +73,8 @@
 int check_config_validity();
 int str2listener(char *str, struct proxy *curproxy, struct bind_conf *bind_conf, const char *file, int line, char **err);
 int cfg_register_section(char *section_name,
-                         int (*section_parser)(const char *, int, char **, int));
+                         int (*section_parser)(const char *, int, char **, int),
+                         int (*post_section_parser)());
 void cfg_unregister_sections(void);
 void cfg_backup_sections(struct list *backup_sections);
 void cfg_restore_sections(struct list *backup_sections);