fix small sh mistakes + add the simple xyz->pos script

utils/converters/xyz2pos.sh

+#!/bin/sh
+
+awk 'BEGIN{ printf "View \"xyz2pos\"{\n";  } { printf "SP(%g,%g,%g){%g};\n", $1, $2, $3, $4; } END {printf "};\n"}'

utils/misc/makedmg.sh

+#!/bin/sh
 
 SRCDIR=gmsh-distrib
 DMGNAME=gmsh.dmg

utils/misc/testgeo.sh

-#/bin/sh
+#!/bin/sh
 
 if [ $# -lt 2 ]; then
   echo "Usage: $0 path program [options]" 1>&2;