ash: parser: Allow newlines within parameter substitution

Upstream commit:

Date: Thu, 22 Mar 2018 21:41:24 +0800
parser: Allow newlines within parameter substitution

    On Fri, Mar 16, 2018 at 11:27:22AM +0800, Herbert Xu wrote:
    > On Thu, Mar 15, 2018 at 10:49:15PM +0100, Harald van Dijk wrote:
    > >
    > > Okay, it can be trivially modified to something that does work in other
    > > shells (even if it were actually executed), but gets rejected at parse time
    > > by dash:
    > >
    > >   if false; then
    > >     : ${$+
    > >   }
    > >   fi
    >
    > That's just a bug in dash's parser with ${} in general, because
    > it bombs out without the if clause too:
    >
    > 	: ${$+
    > 	}

    This patch fixes the parsing of newlines with parameter substitution.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/hush_test/hush-vars/param_expand_alt2.right

@@ -0,0 +1,4 @@
+Unquoted: H H
+Quoted: H
+H
+Ok:0

shell/hush_test/hush-vars/param_expand_alt2.tests

@@ -0,0 +1,7 @@
+echo Unquoted: H${$+
+}H
+
+echo Quoted: "H${$+
+}H"
+
+echo Ok:$?