some work on syntax.test

some work on syntax.test

* module/language/tree-il.scm (tree-il->scheme):
* module/ice-9/psyntax.scm (build-conditional): Attempt to not generate
  (if #f #f) as the second arm of an if, but it doesn't seem to be
  successful.

* module/ice-9/psyntax-pp.scm (syntax-rules): Regenerate.

* test-suite/tests/syntax.test (exception:unexpected-syntax): Change
  capitalization.
  ("unquote-splicing"): Update test.
  ("begin"): Add in second arms on these ifs, to avoid the strange though
  harmless expansion of `if'.
  (matches?): New helper macro.
  ("lambda"): Match on lexically bound symbols, as they will be
  alpha-renamed.