* scm/lily.scm (get-output-module): New function.

* scm/lily.scm (get-output-module): New function.
(output-alist): Remove ,ps-output-expression.

* scm/output-tex.scm (ps-output-expression): New function.

* scm/output-ps.scm (ps-output-expression): Remove.
(header, start-page): Output page metadata.

* lily/paper-outputter.cc (Paper_outputter)[PAGE_LAYOUT]:
initialise output_module_.  Do not write part of header.
(output_scheme)[PAGE_LAYOUT]: Output through output_module_.
(output_header): Output full header.

* scm/define-markup-commands.scm (bigger, smaller): Avoid crash.
FIXME.