added gasdev routine

Framework/Cascade/gasdev.f

+      DOUBLE PRECISION FUNCTION GASDEV(Idum)
+C***********************************************************************
+C     Gaussian deviation
+C***********************************************************************
+      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
+      IMPLICIT INTEGER(I-N)
+      COMMON /RNDMGAS/ ISET
+      SAVE
+      DATA ISET/0/      
+      gasdev=idum
+      IF (ISET.EQ.0) THEN
+1       V1=2.D0*S_RNDM(0)-1.D0
+        V2=2.D0*S_RNDM(1)-1.D0
+        R=V1**2+V2**2
+        IF(R.GE.1.D0)GO TO 1
+        FAC=SQRT(-2.D0*LOG(R)/R)
+        GSET=V1*FAC
+        GASDEV=V2*FAC
+        ISET=1
+      ELSE
+        GASDEV=GSET
+        ISET=0
+      ENDIF
+      RETURN
+      END
+C***********************************************************************
+