Compile in a fresh module by default.

Compile in a fresh module by default.

* module/system/base/compile.scm (make-compilation-module,
  language-default-environment): New procedures.
  (read-and-compile, compile): Have ENV default to
  `(language-default-environment from)'.
  (compile-and-load): Compile in `(current-module)'.

* module/system/repl/common.scm (repl-compile): Explicitly compile in
  the current module so that macro definitions are visible.

* libguile/load.c (kw_env): New variable.
  (do_try_autocompile): Call `compile-file' with `#:env (current-module)'.

* test-suite/tests/compiler.test ("psyntax")["compile uses a fresh module by
  default", "compile-time definitions are isolated"]: New tests.
  ["compile in current module"]: Specify `#:env (current-module)'.
  ["redefinition"]: Adjust.

* test-suite/tests/bytevectors.test (c&e): Explicitly compile in the
  current module so that its imports are visible.