Davix static library crash on CentOS7 about davix

[gbitzes]

Hi Pere,

I confirm I can reproduce the issue, I built ROOT on a CentOS7 VM and get the same crash. Both gUserAgent of TDavixFile and _version of davix are static strings, and vulnerable to the "static initialization order fiasco"..

In this case, gUserAgent is apparently initialized first, and at the time version() is called, _version has not been initialized yet.. The function returns a reference to a memory location containing uninitialized data.

Thanks for the ticket and the fix - I've integrated it to davix.