Merge branch 'rr/forbid-bs-in-ref'

* rr/forbid-bs-in-ref:
  Disallow '\' in ref names

Documentation/git-check-ref-format.txt

@@ -42,6 +42,8 @@ imposes the following rules on how references are named:
 
 . They cannot contain a sequence `@{`.
 
+- They cannot contain a `\\`.
+
 These rules make it easy for shell script based tools to parse
 reference names, pathname expansion by the shell when a reference name is used
 unquoted (by mistake), and also avoids ambiguities in certain