Do not export variables with dot names (re: 8e72608c)

Variables with a dot in their name, such as those declared in
namespace { ... } blocks, are usually stored in a separate tree
with their actual names not containing any dots. But under some
circumstances, including at least direct assignment of a
non-preexisting dot variable, dot variables are stored in the main
sh.var_tree with names actually containing dots. With allexport
active, those could end up exported to the environment. This bug
was also present in previous release versions of ksh.

src/cmd/ksh93/sh/name.c: pushnam():
- Check for a dot in the name before pushing a variable to export.

src/cmd/ksh93/tests/attributes.sh

@@ -728,6 +728,13 @@ exp='typeset -x bar=2'
 got=$(typeset -p bar)
 [[ $got == "$exp" ]] || err_exit 'Variable ${bar} should be exported' \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+.foo=
+.foo.bar=baz
+exp=''
+got=$(env | grep '^\.foo[.=]')
+[[ $got == "$exp" ]] || err_exit 'Variables with dots in name exported' \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+unset .foo.bar .foo
 set +o allexport
 
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