Increate the maximum allowed length of a hostname.

The hostname madagascarsteenplaatschildpad (.uva.nl) doesn't fit in 24,
and hostname(1) accepts up to 64 characters. The RFCs vary, but 63 +
terminating NUL or length-octet + data maximum 64 bytes seen to be
the common ground.

FIXES #514

src/modules/users/UsersPage.h

@@ -68,7 +68,7 @@ private:
     const QRegExp HOSTNAME_RX = QRegExp( "^[a-zA-Z0-9][-a-zA-Z0-9_]*$" );
     const int USERNAME_MAX_LENGTH = 31;
     const int HOSTNAME_MIN_LENGTH = 2;
-    const int HOSTNAME_MAX_LENGTH = 24;
+    const int HOSTNAME_MAX_LENGTH = 63;
 
     bool m_readyFullName;
     bool m_readyUsername;