Merge #7966: http: Do a pending c++11 simplification handling work items

f0188f9 http: use std::move to move HTTPRequest into HTTPWorkItem (Wladimir J. van der Laan)
37b2137 http: Change boost::scoped_ptr to std::unique_ptr in HTTPRequest (Wladimir J. van der Laan)
f97b410 http: Add log message when work queue is full (Wladimir J. van der Laan)
091d6e0 http: Do a pending c++11 simplification (Wladimir J. van der Laan)