[XrdCl] Initial commit

Logging facilities
Testing skeleton
[XrdClTests] Initial commit

Logging facilities
Testing skeleton
[XrdCl] Add environtment support
[XrdCl] Fix default log mask
[XrdCl] Add the possibility to set the log level and log file bu using XRD_LOGLEVEL and XRD_LOGFILE envvars respectively
[XrdCl] Move the default log to the Utils class.
[XrdCl] Allow for setting the log mask through XRD_LOGMASK envvar
[XrdCl] Add stubs for a file representations
[XrdCl] Add trivial and slow URL parser
[XrdClTests] Add tests of the URL parser
[XrdCl] [CMake] Adjust to the new XRootD libs
[XrdCl] Add a scoped descriptor class
[XrdClTests] Add an implementation of a testing server
[XrdClTests] Add an utils class - generate a buffer of random data
[XrdCl] Add a status class for returning error information
[XrdCl] Add a socket implementation (connect and read part only)
[XrdClTests] Add a simple socket reading test
[XrdCl] Factorize out the polling mechanism
[XrdCl] Add unknown error definition
[XrdCl] Fix delete vs. delete []