- Based on a patch by Vlad Grachov, libcurl now uses a new libssh2 0.19

function when built to support SCP and SFTP that helps the library to know
  in which direction a particular libssh2 operation would return EAGAIN so
  that libcurl knows what socket conditions to wait for before trying the
  function call again. Previously (and still when using libssh2 0.18 or
  earlier), libcurl will busy-loop in this situation when the easy interface
  is used!

configure.ac

@@ -1476,6 +1476,10 @@ if test X"$OPT_LIBSSH2" != Xno; then
     LIBSSH2_ENABLED=1
     AC_DEFINE(USE_LIBSSH2, 1, [if libSSH2 is in use])
     AC_SUBST(USE_LIBSSH2, [1])
+
+    dnl check for this function only present in libssh2 0.19+
+    AC_CHECK_FUNCS( libssh2_session_block_directions )
+
   )
 
   if test X"$OPT_LIBSSH2" != Xoff &&