[PATCH] Join with block

This patch adds the ability to give the Array#join method a block like so
 [1,3,2,4].join(' which is X than '){|sep,a,b| a > b ?
sep.sub(/X/,"#{a-b} more") : sep.sub(/X/,"#{b-a} less")}
which produces
 1 which is 2 less than 3 which is 1 more than 2 which is 2 less than 4

The patch is based off the original rb_ary_join and so it handles
nested arrays in the same recursive manner as rb_ary_join:
  [[1,2],[3,4]].join {|sep,a,b| b.class.eql?(Array) ? "->" : ":"}
which produces
  1:2->3:4

The parameters passed into the block are the separator string (sep)
which is the parameter passed to the join method, and the two elements
(a,b) between which sep will be inserted.

The following methods are added/modified:

  * rb_ary_join_m : Calls rb_ary_join or rb_ary_join_block depending
on whether a block is given.
  * rb_ary_join_block: Performs the join using the given block.
  * recursive_join_block: Same functionality as recursive_join but
calls rb_ary_join_block.

Tests are added to sample/test.rb and the definition of
rb_ary_join_block is added to intern.h.

Unfortunately due to some weird transparent proxy errors in South
Africa, I can't log into Rubyforge to add this to the Ruby project
patch tracker. If someone could submit it for me I would appreciate it
(that is if it doesn't get shot out the sky here first)

Thanks,
Farrel