* module/Makefile.am: Add inline.scm.
* module/language/tree-il.scm (pre-order!, post-order!): pre-order! is
new. post-order! existed but was not public. They do destructive tree
traversals of tree-il, and need more documentation. Also, add
predicates to tree-il's export list.
* module/language/tree-il/inline.scm: New file, which expands primitives
into more primitive primitives. In the future perhaps it will not be
necessary, as the general inlining infrastructure will handle these
cases, but for now it's useful.
* module/language/tree-il/optimize.scm: Move post-order! out to better
pastures.
