Map various connection-related errors in XrdCl in XCache all the
way through to the HTTP layer.

This allows a failure to connect to the origin to be represented
with the correct status code ("Bad Gateway"); currently, a down
origin results in a 500 ("Internal Server Error") which is misleading
for users.

Fixes: xrootd#2235

Fixes: xrootd#2236

…ootd#2322

uint16_t to time_t. Since time_t can be 64 bits the Python bindings
need to use unsigned long long.

We test for overflow, but now timeouts use time_t, which may be
64 bits wide, so use 2^65 to force an overflow in that case too.

Reverts commit eb4295e as the hack
introduced there is no longer needed after the current fix.

Fixes: xrootd#2357

In the new SciTag specification, the content of the emitted firefly
should always be created from the data sender point of view.
For HTTP PUT: the srcIp is the client, dstIP is the server,
sentBytes=socketReceivedBytes (~=fileSize),
receivedBytes=socketSentBytes (~=0)
For HTTP GET: the srcIP is the server, dstIP is the client,
sentBytes=socketSentBytes(~=fileSize)
receivedBytes=socketReceivedBytes(~=0)

The distinction is therefore done via the pmark.appname CGI that is
equal to "http-get" if the client request is a GET request or equal to
"http-put" if not.

While RFC 4291 in 2006 introduced "IPv4-compatible IPv6 addresses"
(i.e. ::<ipv4>) if also specified IPv4 mapped addresses (i.e. ::ffff:<ipv4>).
In the intervening years, most implementation no longer support compatible
addresses and mapped address format has replaced it. This update removes
support for compatible address format generation as it's unlikely to work
and substitutes mapped address format as the alternative.

Additional fixes related to the use time_t for timeouts change