Hello all,

I have added a function named `string-split-substring' to the (ice-9
string-fun) module. It acts like `string-split', but taking a substring
instead. It works like this

(string-replace-substring "item-1::item-2::item-3::item-4" "::")
=> ("item-1" "item-2" "item-3" "item-4")

The tests include all the edge cases in the tests for string-split, and
the behavior matches it exactly.

Documentation is also included in the patch.

I have found myself making and using this function numerous times, and
judging by IRC, others find it useful as well. The patch is attached.

~ Vijay