Use correct path to TextTransform.exe depending on the platform.
fe-gtk: Quote path to glib-compile-resources.exe
installer: Use correct path to iscc.exe depending on the platform.
win32: Download deps during installation
Fixes #836.  In gtk_xtext_scroll() always force line integral line boundary.
Fixes #837.  Rewrite gtk_xtext_scroll{down,up}_timeout().
Fixes #836.  Move to line boundary in _scroll{down,up}_timeout() not _scroll().
win32: Download spelling dictionaries from installer