add separate expansion phase, to detwingle things a bit

add separate expansion phase, to detwingle things a bit

* module/language/scheme/expand.scm: New module, implements a separate
  expansion phase, not interleaved with compilation.

* module/language/scheme/amatch.scm: Helper for expand.scm, it's pmatch
  with support for annotated source.

* module/ice-9/Makefile.am (SOURCES): Add annotate.scm to build list --
  early on because it will be used in the compiler.

* module/ice-9/annotate.scm: Fix the printer, default to unstripped
  (whatever that is), and add a deannotator.

* module/system/base/compile.scm (call-with-compile-error-catch): Fix for
  new representation of source locations.

* module/Makefile.am (SCHEME_LANG_SOURCES): Add amatch and expand.