This patch adds the --one (-o) option to git-am, to apply a single 
message in RFC 2822 format, as opposed to an mbox.  With some MUAs it's 
a lot easier to save individual messages than with mboxes, and either 
way the user may want to control the ordering if there are known 
interdependencies.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>