[REST] fix headersonly flag for BINARY responses
[REST] give an appropriate response in warmup phase
[REST] set REST API behind "-rest" option
Merge pull request #5326

5dc713b [REST] set REST API behind "-rest" option (Jonas Schnelli)
78bdc81 [REST] give an appropriate response in warmup phase (Jonas Schnelli)
210eba9 [REST] fix headersonly flag for BINARY responses (Jonas Schnelli)