Fix support for /msg @#chan :hi

005 STATUSMSG defines list of characters prependable to channel name,
but we used simple modes instead.

See
https://tools.ietf.org/html/draft-brocklesby-irc-isupport-03#section-3.16

Fix #272

Thanks to grawity for the link to 005 docs draft, and to carrot for
testing the patch.

include/znc/IRCSock.h

@@ -102,6 +102,7 @@ public:
 	bool IsAuthed() const { return m_bAuthed; }
 	bool IsCapAccepted(const CString& sCap) { return 1 == m_ssAcceptedCaps.count(sCap); }
 	const MCString& GetISupport() const { return m_mISupport; }
+	CString GetISupport(const CString& sKey, const CString& sDefault = "") const;
 	// !Getters
 
 	// This handles NAMESX and UHNAMES in a raw 353 reply

src/IRCNetwork.cpp

@@ -624,7 +624,8 @@ const vector<CChan*>& CIRCNetwork::GetChans() const { return m_vChans; }
 
 CChan* CIRCNetwork::FindChan(CString sName) const {
 	if (GetIRCSock()) {
-		sName.TrimLeft(GetIRCSock()->GetPerms());
+		// See https://tools.ietf.org/html/draft-brocklesby-irc-isupport-03#section-3.16
+		sName.TrimLeft(GetIRCSock()->GetISupport("STATUSMSG", ""));
 	}
 
 	for (unsigned int a = 0; a < m_vChans.size(); a++) {

src/IRCSock.cpp

@@ -1211,6 +1211,15 @@ void CIRCSock::ParseISupport(const CString& sLine) {
 	}
 }
 
+CString CIRCSock::GetISupport(const CString& sKey, const CString& sDefault) const {
+	MCString::const_iterator i = m_mISupport.find(sKey.AsUpper());
+	if (i == m_mISupport.end()) {
+		return sDefault;
+	} else {
+		return i->second;
+	}
+}
+
 void CIRCSock::ForwardRaw353(const CString& sLine) const {
 	vector<CClient*>& vClients = m_pNetwork->GetClients();
 	vector<CClient*>::iterator it;