Improve the XML formatting of responses coming from web interface.

Improve the XML formatting of responses coming from web interface.
Normal responses are sequences of lines of the form "Name: value",
with \r\n as line terminators and an empty line as a response
terminator.

Generi CLI commands, however, do not have such a clean formatting,
and the existing code failed to generate valid XML for them.
Obviously we can only use heuristics here, and we do the following:
- accept either \r or \n as a line terminator, trimming trailing whitespace;
- if a line does not have a ":" in it, assume that from this point on
  we have unformatted data, and use "Opaque-data:" as a name;
- if a line does have a ":" in it, the Name field is not always
  a legal identifier, so replace non-alphanum characters with underscores;

All the above is to be refined as we improve the formatting of
responses from the CLI.

And, all the above ought to go as a comment in the code rather than
just in a commit message...

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@45334 65c4cc65-6c06-0410-ace0-fbb531ad65f3