Revert "Revert "Use @xref more consistently; "See @ref" -> "@xref"""

Revert "Revert "Use @xref more consistently; "See @ref" -> "@xref"""

This reverts commit 59167e2de8a93341cd235d83e034c00be32403f6.
TRT to use reference in Texinfo is to place some punctuation
character after a reference.  This is common both to @ref and
to @xref.  So this is what should be done to fix the changeset,
not to revert it.

(cherry picked from commit 2a314666e4800639a81ff6562395c3d38cb97e7b)