specl/shell: don't force specl's LUA_PATH on subprocesses.

Forcing Specl's internal package.path into a subprocess'
environment will break if the subprocess invokes a Lua
interpreter with a different package.path, especially for a
different Lua version.
* lib/specl/shell.lua (Command._init): Remove LUA_PATH setting.
* specs/spec_helper.lua (run_spec): Pass through LUA_PATH for
inferior Specl processes that `require "spec_helper"`.
* specs/custom_formatters_spec.yaml, specs/specl_spec.yaml:
Add trailing ";;" so we don't override the system package.path.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
configury: bump release number to 10.

* configure.ac (AC_INIT): Bump release number to 10.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>