app_rpt.c: perform_statpost - add verbose text to errors

[mkmer]

Provide text error descriptions from the curl library.
Closes issue #490

[InterLinked1]

Does the error from the library include the number in it? If not, I think we should print both the number and the error name

[mkmer]

Does the error from the library include the number in it? If not, I think we should print both the number and the error name

Actually, there are library errors and web link errors -> that's why I changed it to draft.
We have to capture the response message text in the writefunction to get the web error text.

For web errors it will look something like this:
<http link> failed with code 401 : Unauthorized

For library errors it will look like this:

<http link> failed with error: Could not resolve host: tats.allstarlink.org

I don't believe the library error values make much sense to share (do they?)