* lily/main.cc (setup_paths)[__MINGW32__]: Normalize LILYPONDPREFIX.

* lily/main.cc (setup_paths)[__MINGW32__]: Normalize LILYPONDPREFIX.

* lily/general-scheme.cc (ly:stderr-redirect): Rename from
ly:port-move.  Needs to be stderr-specific on mingw.
Run fixcc.

* lily/general-scheme.cc (ly:port-move): Remove.

* scm/backend-library.scm (postscript->pdf): Remove -dSAFER in
windows.

* lily/main.cc (setup_paths) [ARGV0_RELOCATION]: Reinstate GS_*
variables.  This eliminates the need for a gs.bat wrapper, which
opens a console.

* scripts/lilypond-invoke-editor.scm (running-from-gui?):
* scm/lily.scm (running-from-gui?):
* lily/main.cc[MINGW]: Remove isatty inversion, this is an
artifact of not compiling with -mwindows.

* scm/editor.scm: Define PLATFORM.