#6 Verlet bug

[Philip (Flip) Kromer]

See http://www.fisica.uniud.it/~ercolessi/md/md/node21.html
also
Phys Rev vol 159 #1 p 98 (Verlet paper)

verlet should be
v = newx - oldx / 2 dt
but now the code reads
v = newx - curx / dt

we need good testing -- esp. of melting -- before
committing this change.

flip