[m-rev.] diff: use consisntent key references in the user's guide

[Julien Fischer]

Use consistent key references in the user's guide.

doc/user_guide.texi:
 	s/return/@key{RET}/ in places where the return key
 	is meant.
Julien.

diff --git a/doc/user_guide.texi b/doc/user_guide.texi
index 4dd732c..17e057e 100644
--- a/doc/user_guide.texi
+++ b/doc/user_guide.texi
@@ -4859,7 +4859,7 @@ In some circumstances
  the declarative debugger provides a default answer to the question.
  If this is the case, the default answer will be shown in square brackets
  immediately after the question,
-and simply pressing return is equivalent to giving that answer.
+and simply pressing @key{RET} is equivalent to giving that answer.

  @node Declarative debugging commands
  @subsection Commands
@@ -4867,11 +4867,11 @@ and simply pressing return is equivalent to giving that answer.
  At the above mentioned prompts, the following commands may be given.
  Most commands can be abbreviated by their first letter.

-It is also legal to press return without specifying a command.
+It is also legal to press @key{RET} without specifying a command.
  If there is a default answer (@pxref{Oracle questions}),
-pressing return is equivalent to giving that answer.
+pressing @key{RET} is equivalent to giving that answer.
  If there is no default answer,
-pressing return is equivalent to the skip command.
+pressing @key{RET} is equivalent to the skip command.

  @table @code
  @item yes