typeset: Correct numeric attribute change for floating points (#163)

This commit resolves the following incorrect variable assignments:
$ unset a; typeset -uF a=2; typeset -p a
typeset -X a=0x1.0000000000p+1
$ unset a; typeset -Fu a=2; typeset -p a
typeset -X a=0x1.0000000000p+1
$ unset a; typeset -ulF a=2; typeset -p a
typeset -l -X a=0x1.0000000000p+1
$ unset a; typeset -Ful a=2; typeset -p a
typeset -l -X a=0x1.0000000000p+1
$ unset a; typeset -Eu a=2; typeset -p a
typeset -E -X a=2
$ unset a; typeset -Eul a=2; typeset -p a
typeset -l -E -X a=2

src/cmd/ksh93/bltins/typeset.c:
- If the unsigned option (-u) was provided in conjunction with a
  floating point (-F) then due to a flag collision with NV_UNSIGN
  and NV_HEXFLOAT both having the value of NV_LTOU caused the
  floating point to become a hexadecimal floating point (-X) in
  error. Also, if a -E option flag was followed with a -u option
  then the resulting variable would be both a scientific notation
  and a hexadecimal floating point at the same time.

src/cmd/ksh93/tests/attributes.sh:
- Add regression tests.

Co-authored-by: Martijn Dekker <martijn@inlv.org>

NEWS

@@ -5,6 +5,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
 
 2021-01-24:
 
+- Fixed a bug in 'typeset': combining the -u option with -F or -E caused the
+  variable to become a hexadecimal floating point in error.
+
 - Fixed: an unquoted variable expansion evaluated in a DEBUG trap action caused
   IFS field splitting to be deactivated in code executed after the trap action.
   This bug was introduced in ksh 93t+ 2009-11-30.