Fix crashes caused by 'typeset -RF' (#47)

Variables created with 'typeset -RF' were being treated as
short integers, even though they are actually floating point
values. As a result the following example will cause a crash:

$ typeset -RF foo=1
$ test "$foo"

This is fixed by checking for 'NV_DOUBLE' with 'nv_isattr',
which prevents ksh from treating floating point values as
short integers due to '== NV_INT16P' excluding 'NV_DOUBLE'.
This bugfix was backported from ksh93v- 2013-10-10-alpha.

src/cmd/ksh93/sh/array.c,
src/cmd/ksh93/sh/name.c,
src/cmd/ksh93/sh/nvdisc:
- Avoid treating floating point values as short integers by
  checking for 'NV_DOUBLE' with 'nv_isattr'.

src/cmd/ksh93/tests/types.sh:
- Add a regression test for the 'typeset -RF' crash. The
  crash cannot be replicated if 'typeset -RF' sets 'foo'
  to zero.

src/cmd/ksh93/tests/types.sh

@@ -645,4 +645,9 @@ Bar_t bar
 bar.foo+=(bam)
 [[ ${bar.foo[0]} == bam ]] || err_exit 'appending to empty array variable in type does not create element 0'
 
+# ======
+# 'typeset -RF' should not create variables that cause crashes
+"$SHELL" -c 'typeset -RF foo=1; test $foo' || err_exit 'typeset -RF does not work'
+
+# ======
 exit $((Errors<125?Errors:125))