printf %H: fix/reduce encoding into entities (re: 8477d2ce)

The   entity is not valid in XML, only in HTML. Since we must
be compatible with both, it can't be used. Thanks to Andras Farkas
for the bug report.

In addition, the generation of numeric entities for unprintable
characters was only valid while processing UTF-8 text while in a
UTF-8 locale. In all other conditions it produced invalid results.
This is not worth trying to fix.

Discussion:
https://groups.google.com/d/msgid/korn-shell/CAA0nTRta%3DPbOYduyBv%3DXCzumTcUCU8Lki%3DQQf2O8Erk2BFvO1g%40mail.gmail.com

src/cmd/ksh93/bltins/print.c:
- Remove conversion to   entity.
- Remove conversion of non-graph characters to numeric entities.
  Convert only the 5 semantically meaningful characters: < > & " '

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/sh/string.c:
- We don't need sh_isprint() in print.c anymore, so turn it back
  into a static function.

src/cmd/ksh93/tests/builtins.sh:
- Update and trim regression tests.

src/cmd/ksh93/tests/builtins.sh

@@ -276,7 +276,7 @@ if	[[ $(getopts  $'[+?X\ffoobar\fX]' v --man 2>&1) != *'Xhello world'X* ]]
 then	err_exit '\f...\f not working in getopts usage strings'
 fi
 
-expect='<>"& '	abc'
+expect=$'<>"& '\tabc'
 actual=$(printf '%H\n' $'<>"& \'\tabc')
 [[ $expect == "$actual" ]] || err_exit 'printf %H not working' \
 	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
@@ -295,24 +295,12 @@ actual=$(printf 'foo://ab_c%(url)q\n' $'<>"& \'\tabc')
 case ${LC_ALL:-${LC_CTYPE:-${LANG:-}}} in
 ( *[Uu][Tt][Ff]8* | *[Uu][Tt][Ff]-8* )
 	# HTML encoding UTF-8 characters
-	expect='what?'
-	actual=$(printf %H 'what?')
-	[[ $actual == "$expect" ]] || err_exit 'printf %H: ASCII characters' \
-				"(expected $expect; got $actual)"
-	expect='عندما يريد العالم أن &#8234;يتكلّم &#8236; ، فهو يتحدّث بلغة يونيكود.'
-	actual=$(printf %H 'عندما يريد العالم أن ‪يتكلّم ‬ ، فهو يتحدّث بلغة يونيكود.')
-	[[ $actual == "$expect" ]] || err_exit 'printf %H: Arabic UTF-8 characters' \
-				"(expected $expect; got $actual)"
 	expect='正常終了 正常終了'
 	actual=$(printf %H '正常終了 正常終了')
 	[[ $actual == "$expect" ]] || err_exit 'printf %H: Japanese UTF-8 characters' \
 				"(expected $expect; got $actual)"
-	expect='« l’abîme de mon&nbsp;métier… »'
-	actual=$(printf %H '« l’abîme de mon métier… »')
-	[[ $actual == "$expect" ]] || err_exit 'printf %H: Latin UTF-8 characters' \
-				"(expected $expect; got $actual)"
-	expect='?&#134;???'
-	actual=$(printf %H $'\x86\u86\xF0\x96\x76\xA7\xB5')
+	expect='w?h?á?t??'
+	actual=$(printf %H $'w\x80h\x81\uE1\x82t\x83?')
 	[[ $actual == "$expect" ]] || err_exit 'printf %H: invalid UTF-8 characters' \
 				"(expected $expect; got $actual)"
 	# URL/URI encoding of UTF-8 characters