Merge branch 'cc/replace'

* cc/replace:
  t6050: check pushing something based on a replaced commit
  Documentation: add documentation for "git replace"
  Add git-replace to .gitignore
  builtin-replace: use "usage_msg_opt" to give better error messages
  parse-options: add new function "usage_msg_opt"
  builtin-replace: teach "git replace" to actually replace
  Add new "git replace" command
  environment: add global variable to disable replacement
  mktag: call "check_sha1_signature" with the replacement sha1
  replace_object: add a test case
  object: call "check_sha1_signature" with the replacement sha1
  sha1_file: add a "read_sha1_file_repl" function
  replace_object: add mechanism to replace objects found in "refs/replace/"
  refs: add a "for_each_replace_ref" function

parse-options.h

@@ -145,6 +145,10 @@ extern int parse_options(int argc, const char **argv, const char *prefix,
 extern NORETURN void usage_with_options(const char * const *usagestr,
                                         const struct option *options);
 
+extern NORETURN void usage_msg_opt(const char *msg,
+				   const char * const *usagestr,
+				   const struct option *options);
+
 /*----- incremental advanced APIs -----*/
 
 enum {