Correct the documentation for set_passwd_cb
diff --git a/doc/pyOpenSSL.tex b/doc/pyOpenSSL.tex
index 86d54f0..a6380e3 100644
--- a/doc/pyOpenSSL.tex
+++ b/doc/pyOpenSSL.tex
@@ -790,14 +790,14 @@
\begin{methoddesc}[Context]{set_passwd_cb}{callback\optional{, userdata}}
Set the passphrase callback to \var{callback}. This function will be called
-when a private key with a passphrase is loaded.
-\var{callback} should take a boolean argument \var{repeat} and an arbitrary
-argument \var{data} and return the passphrase entered by the user. If
-\var{repeat} is true then \var{callback} should ask for the passphrase twice
-and make sure that the two entries are equal. The \var{data} argument is the
-\var{userdata} variable passed to the \method{set_passwd_cb} method. If an
-error occurs, \var{callback} should return a false value (e.g. an empty
-string).
+when a private key with a passphrase is loaded. \var{callback} must accept
+three positional arguments. First, an integer giving the maximum length of
+the passphrase it may return. If the returned passphrase is longer than
+this, it will be truncated. Second, a boolean value which will be true if
+the user should be prompted for the passphrase twice and the callback should
+verify that the two values supplied are equal. Third, the value given as the
+\var{userdata} parameter to \method{set_passwd_cb}. If an error occurs,
+\var{callback} should return a false value (e.g. an empty string).
\end{methoddesc}
\begin{methoddesc}[Context]{set_session_id}{name}