Merge pull request #2050 from yyhrnk/fix/bip390-musig-rawtr-usage

BIP-390: allow musig() under rawtr()

Author: murchandamus

bip-0390.mediawiki

@@ -35,8 +35,8 @@ and [[bip-0389.mediawiki|BIP-389]].
 
 ===<tt>musig(KEY, KEY, ..., KEY)</tt>===
 
-The <tt>musig(KEY, KEY, ..., KEY)</tt> expression can only be used inside of a <tt>tr()</tt>
-expression as a key expression. It additionally cannot be nested within another <tt>musig()</tt>
+The <tt>musig(KEY, KEY, ..., KEY)</tt> expression can only be used inside of a <tt>tr()</tt> or
+<tt>rawtr()</tt> expression as a key expression. It additionally cannot be nested within another <tt>musig()</tt>
 expression. Participant public keys may be repeated. The aggregate public key is produced
 by using the <tt>KeyAgg</tt> algorithm on all KEYs specified in the expression after performing all
 specified derivation. As with script expressions, KEY can contain child derivation specified by