monoMDS could crash with huge input dissimilarites

monoMDS needed to set a guard dissimilarity which is longer than
observed dissimilarity, and this could fail if observed dissimilarities
were huge (in the issue #152 dissimilarities were of magnitude 2e85),
and this could crash monoMDS.

Fixes issue #152 reported in github.

src/monoMDS.f

@@ -10,6 +10,10 @@ SUBROUTINE monoMDS (NOBJ, NFIX, NDIM, NDIS, NGRP,
 C 1.01 April 6, 2011  - added argument STRS(NGRP) to return the stress
 C                       for each of the NGRP groups of dissimilarities
 C                       i.e., from each separate regression.
+C 1.02 January 7, 2016 - fixed bug in MONREG so that huge 
+C                        dissimilarities are correctly handled in
+C                        creating the initial partition for monotone 
+C                        regression with primary tie treatment.
 C
 C Written by Dr. Peter R. Minchin
 C            Department of Biological Sciences
@@ -596,9 +600,9 @@ SUBROUTINE CLCSTP (STEP,IT,SFGR,STRESS,COSAV,ACOSAV,SRATIO,
 C
       ELSE
         FACTR1=4.0**COSAV
-        FACTR2=1.6/( (1.0+(MIN(1D0,SRATAV))**5) *
+        FACTR2=1.6/( (1.0+(MIN(1.0,SRATAV))**5) *
      .    (1.0+ACOSAV-ABS(COSAV)) )
-        FACTR3=SQRT(MIN(1D0,SRATIO))
+        FACTR3=SQRT(MIN(1.0,SRATIO))
         STEP=STEP*FACTR1*FACTR2*FACTR3
       ENDIF
       RETURN
@@ -900,7 +904,9 @@ SUBROUTINE MONREG (DISS,DIST,DHAT,IIDX,JIDX,IWORK,N,ITIES)
         IF (I.LT.N) THEN
           DNEXT=DISS(I+1)
         ELSE
-          DNEXT=DISS(I)+1.0
+C---Bug fix January 7, 2016: correctly handles huge dissimilarities
+C          DNEXT=DISS(I)+1.0
+          DNEXT=DISS(I)*2.0
         END IF
         IF (ABS(DNEXT-DISS(I)).GT.TOLER) THEN
 C---NTIE is the number of DISS values in the current group of tied values