Fix lock file errors when using a BEAMnrc library

Call beam_finish from beamlib_finish with a different ientry value of 3.
This signals that the BEAM source library is done and that there is no
need to call egs_pjo_finish, which tries to access the lock file for
regular BEAMnrc parallel runs.

Previously, while testing the uniform run control object in Mortran
apps, fort.* files were left behind in the DOSXYZnrc app folder when
using BEAMnrc libraries as a source of particles. This occurred whether
or not the simulation relied on a lock file. Interestingly, the problem
was noticed using gcc 7.5 on Ubuntu 18.04, but it does not occur with
gcc 4.8 on CentOS 7.

These spurious fort.* files contained error messages from the BEAM
library source, reporting a failure to rewind the lock file. The error
message was traced to the egs_pjob_finish routine attempting to rewind
and read the lock file.

The bug occurs because a BEAM library source does not create a lock
file, yet at the end of a parallel run beamlib_finish calls
beam_finish(ientry), with the same ientry=1 argument used in regular
BEAMnrc simulations (which create a lock file).

This bug does not affect the simulation results since it since it aborts
the parallel job when it was already done, with a call to $egs_fatal
which attempts to ouput an error message to an output file that is
already closed.

HEN_HOUSE/omega/beamnrc/beam_lib.mortran

@@ -267,8 +267,8 @@ subroutine beamlib_finish;
 implicit none;
 "write .egsdat file if requested"
 call beam_write_dat;
-call beam_finish(1);
-"call with 1 to signify end of beam lib run"
+call beam_finish(3);
+"call with 3 to signify end of beam lib run"
 return; end;
 
 "below is a dummy xvgrplot subroutine for use with BEAM shared

HEN_HOUSE/omega/beamnrc/beamnrc.mortran

@@ -5016,10 +5016,10 @@ ITMAX=3+LNEXC+LNINC;
 
 return; end;
 
-subroutine beam_finish(ientry);
+subroutine beam_finish(i_entry);
 implicit none;
 
-$INTEGER ientry,egs_open_file;
+$INTEGER i_entry, ientry, egs_open_file;
 
 ;COMIN/SCORE,SOURCE,STACK,IO_INFO,RANDOM,USER,CMs,EGS-IO,UPHIOT,TIMING-INFO,
        RWPHSP/;
@@ -5038,6 +5038,8 @@ $INTEGER I,I1,I2,I3,I4,IT,ITMAX,IERR,NUMIND,COVIND;
 
 $DECLARE_TIMING_VARIABLES;
 
+$LOGICAL is_beam_src;
+
 external combine_results;
 
 #ifdef HAVE_C_COMPILER;
@@ -5046,6 +5048,16 @@ integer n_job;
 #endif;
 
 is_finished = .false.;
+is_beam_src = .false.;
+
+"Calling from a BEAM source library"
+IF (i_entry = 3)[
+   is_beam_src = .true.;
+   ientry = 1;
+]
+ELSE["Proceed as usual"
+  ientry = i_entry;
+]
 
 "*******************************************************************************
 "
@@ -5485,7 +5497,7 @@ call egs_finish;     " Finish the simulation "
 
 #ifdef HAVE_C_COMPILER;
 ;
-IF( n_parallel > 0 & ~is_finished ) [
+IF( n_parallel > 0 & ~is_finished & ~is_beam_src ) [
     call egs_pjob_finish(n_job);
     IOUTLIST=egs_open_file(IOUTLIST,0,1,'.egslst');
     IF( n_job = 0 ) [