On a way to factoring out OpenSSL support to a standalone file to ease
addition of other crypto libraries support in the future, move helpers
providing BASE64 encoding and decoding to crypto-utils.{c,h}. OpenSSL-
related functionality is moved to crypto-utils-openssl.c.
Add new functions to be implemented by crypto backends:
* tr_base64_encode_impl - encode from binary to BASE64,
* tr_base64_decode_impl - decode from BASE64 to binary.
Change `tr_base64_encode` and `tr_base64_decode` functions to expect
non-negative input data length which is considered real and never adjusted.
To process null-terminated strings (which was achieved before by passing 0
or -1 as input data length), add new `tr_base64_encode_str` and
`tr_base64_decode_str` functions which do not accept input data length as
an argument but calculate it on their own.
1. add the option the code to be used under GPLv2 or GPLv3; previously only GPLv2 was allowed
2. add the "proxy option" as described in GPLv3 so we can add future licenses without having to bulk-edit everything again :)
3. remove the awkward "exception for MIT code in Mac client" clause; it was unnecessary and confusing.
Mike Gelfand