bug in drop()

[RobinHankin]

> drop(abc(1:5),as.free('a'))
[1] 0       b       b.c     b.c.d   b.c.d.e
> drop(abc(1:5),'a')
[1] a         a.b       a.b.c     a.b.c.d   a.b.c.d.e
> 

It is reasonable to expect both lines above to return the same thing. But the second is clearly wrong.

Also:

> keep(abc(1:5),'a')
[1] 0 0 0 0 0
> keep(abc(1:5),as.free('a'))
[1] a a a a a
> 

[RobinHankin]

fixed by b20e92ebeca8486461b8140f5fa0fc2a6046eadf