[PATCH] Give the user a hint for how to continue in the case that git-am fails because it requires user intervention

Give the user a hint for how to continue in the case that git-am fails 
because it requires user intervention.

Signed-off-by: Robert Shearman <redacted>

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When git-am fails because it needs user intervention, the user may not 
know what they need to do to continue with applying the mailbox. This 
patch gives them a hint to use git-am (as they may have started the 
operation from another tool, such as git-rebase). As the threeway, 
interactive and dotest options are not persisted, the user may also 
forget to include them (or not realise at all that they should be 
included), so we should also tell the user to include these options if 
they were orignally specified.

  git-am.sh |   26 +++++++++++++++++++++++---
  1 files changed, 23 insertions(+), 3 deletions(-)