Console IO for password protected sources fails under Windows+IDL

[cpiker]

The default das_term_prompt function in credentials.c is expecting ASCII input for username and password data, however the console could be set to use any random code page.

In addition, the das_b64_encode function (also in credentials.c) seems to produce illegal base64 strings for windows console input.

To replicate the problem:

1. Start IDL
2. Do not call das2c_credload()
3. In order to trigger console IO, access a password protected data source.
4. View the resulting hash via das2c_creds(), it will not be a legal base 64 encoding.

Though the bug replication procedure above uses IDL, and thus the Das2DLM, the cause seems to be in das2C code.