git-submodule.sh: properly initialize shell variables

git-submodule inherits variables from the environment it is started in, expects the internal variables init= and recursive= to have an empty value, but doesn't initialize them appropriately. Thanks to the selftests, this can be reproduced through init=1 make test recursive=1 make test With this commit the variables are initialized, and the selftests succeed even if these variables have some values in the environment. The bug was discovered through the Debian autobuilders http://bugs.debian.org/569594 Signed-off-by: Gerrit Pape <pape@smarden.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>