Add CURLE_OPERATION_TIMEDOUT (28) from libcurl

This is the same constant as the "deprecated" CURLE_OPERATION_TIMEOUTED
which is not in libcurl documentation anymore.
Add test for E_OPERATION_TIMEDOUT
Delete unneeded version specification
Merge pull request #93 from p-push/e_operation_timedout

Add CURLE_OPERATION_TIMEDOUT (28) from libcurl