MPH_timer - collect timing info in different channels.

This function collects timing info in different channels.

    Usage:
    channel 0 is the default channel, using init_time.
    ---------------------------------------------------------
    timer calls to walk-clock dclock(), and do the following:
    ---------------------------------------------------------
    flag=0  : Sets initial time; init all channels.
    flag =1 : Calculates the most recent time interval; accrues it 
              to the specified channel (default 0);  Returns it to 
              calling process.
    flag =2 : Calculates the most recent time interval; accrues it 
              to the specified channel (default 0);  Returns the 
              curent total time in the specified channel.
    ---------------------------------------------------------

REVISION HISTORY:

       2001-Nov-19 -- add PROTEX convention
       2001-May-20 -- first prototype

INTERFACE:

       real (kind=8) function MPH_timer (flag, channel)

USES:

       implicit none

INPUT PARAMETERS:

       integer :: flag, channel

OUTPUT PARAMETERS:

       ! real (kind=8) MPH_timer (flag, channel)

LOCAL VARIABLES:

       real (kind=8) :: new_time, delta_time, MPI_Wtime

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