Fixed failing unit tests and catch exception in BeginSentTo's asynchronous callback

[KristianVirkus]

Please see commit messages for details. Sorry for the automatic white space corrections by a plugin.

[KristianVirkus]

The reason why some of the unit tests failed on my machine is that my OS language is not en-?? which of course leads to differently localised default exception messages. The original unit tests had checked for the en-?? messages.

[lextm]

@KristianVirkus can you sign the CLA at http://www.clahub.com/agreements/lextm/sharpsnmplib? Thanks in advance.

[CLAassistant]

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