Include thelp32.h, psapi.h and coding.h.

Include thelp32.h, psapi.h and coding.h.
(_MEMORYSTATUSEX, _PROCESS_MEMORY_COUNTERS_EX): New struct declarations.
(CreateToolhelp32Snapshot_Proc, Process32First_Proc, Process32Next_Proc): New
typedefs.
(g_b_init_create_toolhelp32_snapshot, g_b_init_process32_first)
(g_b_init_process32_next, g_b_init_open_thread_token)
(g_b_init_impersonate_self, g_b_init_revert_to_self)
(g_b_init_get_process_memory_info, g_b_init_global_memory_status)
(g_b_init_get_process_working_set_size)
(g_b_init_global_memory_status_ex): New static variables.
(globals_of_w32): Initialize them.
(create_toolhelp32_snapshot, process32_first, process32_next)
(open_thread_token, impersonate_self, revert_to_self)
(get_process_memory_info, get_process_working_set_size)
(global_memory_status, global_memory_status_ex): New wrapper functions.
(w32_list_system_processes, w32_system_process_attributes)
(enable_privilege, restore_privilege, ltime, process_times): New functions.
(convert_time_raw): New function.
(convert_time): Remove conversion of FILETIME into time in 100 nsec units,
call convert_time_raw instead.