Changes name of ___USE_SMP and ___gvm_struct

 * ___USE_SMP    => ___MULTIPLE_VMS vs ___SINGLE_VM
 * ___gvm_struct => ___vm_state_struct
 * ___GVM        => ___VMSTATE

 On branch para
 Changes to be committed:
    modified:   include/gambit.h.in
    modified:   lib/mem.c
    modified:   lib/os_base.c
    modified:   lib/os_dyn.c
    modified:   lib/os_files.c
    modified:   lib/os_io.c
    modified:   lib/os_shell.c
    modified:   lib/os_time.c
    modified:   lib/os_tty.c
    modified:   lib/setup.c
Enables dynamic allocation of files_module structures when using
___MULTIPLE_VMS. Currently memory is never reclaimed, but it doesn't
need to since the only vm is never reclaimed.

 On branch para
 Changes committed:
    modified:   include/gambit.h.in
    modified:   lib/_kernel.scm
    modified:   lib/os_files.c
Adds dynamic allocation for most os_* struct.

TODO:
  * Deallocation
  * os_base.c
  * Move ___*_MOD definitions to the corresponding header file.

 On branch para
 Changes to be committed:
    modified:   lib/main.c
    modified:   lib/os_dyn.c
    modified:   lib/os_files.c
    modified:   lib/os_io.c
    modified:   lib/os_shell.c
    modified:   lib/os_time.c
    modified:   lib/os_time.h
    modified:   lib/os_tty.c
    modified:   lib/os_tty.h
    modified:   lib/setup.c
Moves ___*_MOD definitions to their corresponding header file.

Adds non-functionnal functions to manage ___BASE_MOD dynamically. It
seems to not work because ___create_base_mod allocates memory with
___alloc_mem which requires the existence of ___BASE_MOD. Cyclic
dependencies (yeah! :D).

 On branch para
 Changes committed:
   (use "git reset HEAD <file>..." to unstage)

    modified:   lib/os_base.c
    modified:   lib/os_base.h
    modified:   lib/os_dyn.c
    modified:   lib/os_dyn.h
    modified:   lib/os_files.c
    modified:   lib/os_files.h
    modified:   lib/os_io.c
    modified:   lib/os_io.h
    modified:   lib/os_shell.c
    modified:   lib/os_shell.h
    modified:   lib/os_time.h
    modified:   lib/os_tty.c
    modified:   lib/os_tty.h
    modified:   lib/setup.c