Return correct content-range header

[PerilousApricot]

According to the HTTP spec, the response from a "Range" request should have a
"content-range" header in the form of "range_begin-range_end/doc_length". But
xrootd currently returns the length of the range intead of the range of the whole
file. Pass in the length of the file and additionally change the printf string since the
file size is stored in a long long

[bbockelm]

Just tested this on a local server:

$ curl -H 'Range: bytes=0-5' -v http://host.example.com:8000//tmp/xrootd_export/hello_world
* About to connect() to host.example.com port 8000 (#0)
*   Trying 1:2:3:4:5:6:7:8...
* Connected to host.example.com (1:2:3:4:5:6:7:8) port 8000 (#0)
> GET //tmp/xrootd_export/hello_world HTTP/1.1
> User-Agent: curl/7.29.0
> Host: host.example.com:8000
> Accept: */*
> Range: bytes=0-5
> 
< HTTP/1.1 206 Partial Content
< Connection: Keep-Alive
< Content-Length: 6
< Content-Range: bytes 0-5/14
< 

Looks good to me! Would be reasonable to squeeze this in for 4.9.0.

[ffurano]

Absolutely agree, that was actually a bug