[CM] Snd 23.9

[bil at ccrma.Stanford.EDU]

Snd 23.9:

s7: added optional let argument to immutable? and immutable!
     finally added error checks to the tree-* functions
       see lint.scm for the previous versions
     s7_make_c_pointer_wrapper_with_type
     ' (apostrophe) now is (#_quote ...) and similarly
       for the quasiquote helpers, apply-values, and list-values.

Thanks!: Norman Gray