Disables dynamic allocation of os_* structs and adds dynamic allocation
of vm_state_struct.

 On branch para
 Changes committed:

    modified:   include/gambit.h.in
    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.c
    modified:   lib/os_time.h
    modified:   lib/os_tty.c
    modified:   lib/os_tty.h
    modified:   lib/setup.c
Set ___time_mod to be a vmstate attribute when use ___MULTIPLE_VMS is
set.

 On branch para -- Changes committed:
    modified:   include/gambit.h.in
    modified:   lib/os_base.h
    modified:   lib/os_time.c
    modified:   lib/os_time.h
    modified:   lib/setup.c
Adds rough thread api. It is still unused and probably buggy.

 On branch para
 Changes committed:
     new file:   lib/os_thread.c
     new file:   lib/os_thread.h
Fix ___os_thread_proc typedef.
Adds mockup for windows thread implementation alongside pthreads.

 On branch para
 Changes committed:
    modified:   lib/os_thread.c
    modified:   lib/os_thread.h