lnotab-based tracing is very complicated and isn't documented very well.  There
were at least 3 comment blocks purporting to document co_lnotab, and none did a
very good job. This patch unifies them into Objects/lnotab_notes.txt which
tries to completely capture the current state of affairs.

I also discovered that we've attached 2 layers of patches to the basic tracing
scheme. The first layer avoids jumping to instructions that don't start a line,
to avoid problems in if statements and while loops.  The second layer
discovered that jumps backward do need to trace at instructions that don't
start a line, so it added extra lnotab entries for 'while' and 'for' loops, and
added a special case for backward jumps within the same line. I replaced these
patches by just treating forward and backward jumps differently.

the dedicated C type `pid_t` instead of a C `int`. Some platforms have
a process identifier type wider than the standard C integer type.

are added later, and skip the existing test if SSL is not available.

the socket.  Patch by Farhan Ahmad, test by Marcin Bachry.

deadlock. add a warning to subprocess docs about this, similar to Popen.wait's.
refs http://bugs.jython.org/issue1351

Rename TestCase._result to _resultForDoCleanups to avoid potential clashes in TestCase subclasses. Issue 6072.

a code object.

to make it possible to use pydoc to get access to the language reference.

That is, without this patch the folllowing won't work:

   >>> help('if')

made it try to set the line number from the trace callback for a 'call' event.
This patch makes the error message a little more helpful in that case, and
makes it a little less likely that a future editor will make the same mistake
in test_trace.