Fix breakage of SRFI-4 C accessors

* libguile/srfi-4.c (DEFINE_SRFI_4_C_FUNCS): Fix bad assumption that
  width was a byte width.  Thanks very much to Barry Fishman for the
  report, and to Daniel Llorens for tracking it down.

* test-suite/standalone/Makefile.am (test_srfi_4_CFLAGS):
* test-suite/standalone/test-srfi-4.c: Add test.
simple-format: Don't assume the current output port is valid.

* libguile/print.c (scm_simple_format): Validate the current output
  port.
Fix (rnrs io simple) to open file ports in textual mode.

Fixes <http://bugs.gnu.org/17044>.
Reported and diagnosed by Xin Wang <dram.wang@gmail.com>.

* module/rnrs/io/simple.scm (open-input-file, open-output-file): Pass
  missing buffer-mode argument to open-file-{input,output}-port.
  Previously, (native-transcoder) was incorrectly passed as the
  buffer-mode argument, so no transcoder was provided, thus creating a
  binary port.
tests: Check 'simple-format' with closed current-output-port.

This is a follow-up to e26ab06.

* libguile/print.c (scm_simple_format): Pass 1 to
  SCM_VALIDATE_OPORT_VALUE, for 'destination'.
* test-suite/tests/format.test ("simple-format"): Add test.
tests: Add #undef NDEBUG when using <assert.h>.

* test-suite/standalone/test-loose-ends.c,
  test-suite/standalone/test-num2integral.c,
  test-suite/standalone/test-round.c,
  test-suite/standalone/test-scm-c-bind-keyword-arguments.c,
  test-suite/standalone/test-scm-c-read.c,
  test-suite/standalone/test-scm-values.c,
  test-suite/standalone/test-smob-mark.c,
  test-suite/standalone/test-srfi-4.c: Add #undef NDEBUG.
Update NEWS.
Bump version number for 2.0.11.

* GUILE-VERSION (GUILE_MICRO_VERSION): Increment.
  (LIBGUILE_INTERFACE_REVISION): Increment.