AMI Originate - Update/fix multiple variable support

[exvito]

Changing AMI Originate to send multiple variables as multiple entries of the "Variable" key, as per documentation of Asterisk 1.4 onwards.

Now sends:

> Action: Originate
> Variable: VAR_A=va
> Variable: VAR_B=vb
> ...

Instead of the single key with comma-separated variables:

> Action: Originate
> Variable: VAR_A=va,VAR_B=vb
> ...

Motives:

• Asterisk 1.4, 1.8 and 11 were not responding correctly/consistently:
  • AMI Action "GetVar" was returning no values for any of the variables.
  • CLI "core show channel " showing an odd-looking "VAR_A=va,VAR_B=vb" in a single line in the "Variables:" section.
  • chan_sip seemed to be grabbing the "SIPADDHEADERS" variable we were using, to some degree of success.
• Following spec/docs, of course.

PS: Made possible based on the work from PR #24 which allows sending AMI Actions with repeated "keys".

Final notes:

• Not sure where the comma-separated implementation came from and eventual backward compatibility requirements. Should that be addressed? Maybe Asterisk 1.2 and earlier have an AMI/1.0 implementation distinct from 1.4's? Any pointers?
• Again, per docs, the current implementation seems to be missing valid keys ("earlymedia" and "codecs", for example); for the purpose of this PR and, of course, to restrcit the commit changes, all of these were left unchanged. It may make sense to review/revamp originate's implementation (again, this may be related to older AMI implementations).
• Last but not least, as a side comment, the new sendMessage implementation, from PR #24, includes lots of code duplication and could be improved. Would you be willing to accept such a proposal?

Thanks for your review and feedback.

[exvito]

Owners,

Any feedback?

Thanks again.

[russellb]

Looks good, thanks!

[exvito]

Great. Thanks.