[regress/putty-kex.sh regress/putty-transfer.sh] Downgrade disabled
interop tests from FATAL error to a warning. Allows some interop
tests to proceed if others are missing necessary prerequisites.
[regress/Makefile regress/test-exec.sh regress/putty-ciphers.sh]
[regress/putty-kex.sh regress/putty-transfer.sh regress/ssh2putty.sh]
basic (crypto, kex and transfer) interop regression tests against putty
To run these, install putty and run "make interop-tests" from the build
directory - the tests aren't run by default yet.