Many functions now support "dir_fd" and "follow_symlinks" parameters;
some also support accepting an open file descriptor in place of of a path
string.  Added os.support_* collections as LBYL helpers.  Removed many
functions only previously seen in 3.3 alpha releases (often starting with
"f" or "l", or ending with "at").  Originally suggested by Serhiy Storchaka;
implemented by Larry Hastings.

Patch by Yury Selivanov.

Mostly documentation changes; the code changes are clarifications,
not semantic changes.

Issue #14837: SSL errors now have `library` and `reason` attributes describing precisely what happened and in which OpenSSL submodule.
The str() of a SSLError is also enhanced accordingly.

NOTE: this commit creates a reference leak.  The leak seems tied to the
use of PyType_FromSpec() to create the SSLError type.  The leak is on the
type object when it is instantiated:

>>> e = ssl.SSLError()
>>> sys.getrefcount(ssl.SSLError)
35
>>> e = ssl.SSLError()
>>> sys.getrefcount(ssl.SSLError)
36
>>> e = ssl.SSLError()
>>> sys.getrefcount(ssl.SSLError)
37

not contested, similar to what _thread.RLock already has.

timezone instance corresponding to the system local timezone when
called with no arguments.