* module/ice-9/popen.scm (open-pipe*): Hack around the lack of an
after-gc hook, and pump the pipes guardian here in the procedure that
adds to the guardian.
* module/ice-9/boot-9.scm (*repl-level*): New global fluid, moved here
from (system repl common).
(batch-mode?): Reimplement in terms of *repl-level*.
(ensure-batch-mode!): A replacement for set-batch-mode?!.
* module/ice-9/deprecated.scm (set-batch-mode?!): Deprecate.
* module/ice-9/popen.scm (open-process): Use ensure-batch-mode!.
* module/ice-9/scm-style-repl.scm (error-catching-loop): Override
ensure-batch-mode!.
* module/system/repl/common.scm: Remove *repl-level*.
Moved ice-9/ and oop/ under module/, with the idea being that we have
only scheme under module/. Adjusted configure.in and Makefile.am
appropriately. Put oop/ at the end of the compilation order.