!SetPaths sets your C$Path environment variable, so that the
Acorn C compiler uses the header files that are part of the Acorn
C/C++ product, and adds !SetPaths.Lib32 to Run$Path so that the
programs within it can be found.

It also sets the following paths to allow the shared makefiles to
build applications with the DDE:
  CLIB$Path
  C$Path
  C$LibRoot
  Makefiles$Path
  RISCOSLib$Path
  RISC_OSLib$Path
  TCPIPLibs$Path
  Hdr$Dir
  Hdr$Path
  LocalRes$Path
  Install$Dir

Finally, it Filer_Boots the applications in the Apps.DDE directory,
so that files which are created or used by applications such as
!ResEd, !Make and !DDT may be used without the filer having seen them.
