git-archimport: support empty summaries, put summary on a single line.
git-archimport: support empty summaries, put summary on a single line.

Don't fail if the summary line in an arch commit is empty.  In this case,
try to use the first line in the commit message followed by an ellipsis.
In addition, if the summary is multi-line, it is joined on a single line.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git