Merge branch 'pk/rebase-in-c-3-acts'

Rewrite "git rebase" in C.

* pk/rebase-in-c-3-acts:
  builtin rebase: stop if `git am` is in progress
  builtin rebase: actions require a rebase in progress
  builtin rebase: support --edit-todo and --show-current-patch
  builtin rebase: support --quit
  builtin rebase: support --abort
  builtin rebase: support --skip
  builtin rebase: support --continue

strbuf.h

@@ -190,6 +190,9 @@ void strbuf_ltrim(struct strbuf *sb);
 /* Strip trailing directory separators */
 void strbuf_trim_trailing_dir_sep(struct strbuf *sb);
 
+/* Strip trailing LF or CR/LF */
+void strbuf_trim_trailing_newline(struct strbuf *sb);
+
 /**
  * Replace the contents of the strbuf with a reencoded form.  Returns -1
  * on error, 0 on success.