Slurring out of an alternative back to the beginning of a volta

[Garrett Fitzgerald]

I managed to get rid of the "unterminated slur" message when slurring
back to the beginning of a repeat with the following code, based on
earlier suggestions on the list. Sharing FWIW, if anything.

\alternative { { a8 r r e16(
                   \afterGrace f16 {\once \override Rest #'transparent = ##t 
g8\rest)} | }
                 { a4 r |}
               }