If the user has configured a value for SHELL_PATH then
be sure to use it for any generated scripts instead of
hard-coding /bin/sh.
The first line of the script is handled specially, but
the embedded #!/bin/sh line in the here document will
not be automatically updated unless it uses @SHELL_PATH@.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>