* scm/stencil.scm (write-system-signature): better escaping.

* scm/stencil.scm (write-system-signature): better escaping.

* scm/framework-ps.scm (output-framework): dump-signatures support
for plain output.

* GNUmakefile.in: create web-signature-root/ too

* make/lilypond-vars.make (LILYPOND_BOOK_FLAGS): add -ddump-signatures.

* scm/framework-ps.scm (write-preamble): redefine mark_URI to nop
for -dno-point-and-click