Check for libcurl's return codes when appropriate.

Check for libcurl's return codes when appropriate.

Depending on the option being set by curl_easy_setopt, a return value
different from CURL_OK can be returned (the same applies to curl_multi_*
and CURLM_OK).

This commit checks the return value from those calls and usually
displays an error message with ERR() and returns -- in some cases, an
error is shown but the function does not immediately return.

A few lines of code have also been moved around in order to make
returning from functions as harmless as possible.

By: Raphael Kubo da Costa <kubo@profusion.mobi>

git-svn-id: http://svn.enlightenment.org/svn/e/trunk/ecore@53275 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33