#264 Q.931 support for multiple occurences of same IE type

[Simon Zwahlen]

In our application we have to deal with Q.931 extensions of Avaya Communication Manager. This PBX sends multiple Facility Information Elements in a Q.931 message.

As the current data structure in the Q931 code can't handle multiple occurrences of the same type, we had to re-implement this to use a PLIST instead of a PDICTIONARY.

This approach probably has a slightly reduced performance than the current one.

Nevertheless I wanted to share this code, perhaps it's interesting for the project or other users.

This patch converts the IE storage to a PLIST. It leaves the current API and is fully backwards compatible, but adds some methods to work with the said information elements:
- GetIEList to get a list of all IE's with this type
- AppendIE to append a IE to the list

[Simon Zwahlen]

Patch against current HEAD

[Robert Jongbloed]

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I have implemented this in a different way that I think is simpler and does not compromise performance as much. Please check out the lastest opalvoip trunk revision.