Copy Sun-specific inclusion of <alloca.h> from 2.7 maint to trunk; it seems to not have been merged to py3k.

Make urllib tests pass for now.  Will figure out what the correct semantics should be after release.

The concrete types are for internal use (registration).
We are not trying to resurrect the types module
in collections.

Part of #7245: when KeyboardInterrupt is raised while defining commands, restore the old commands instead of producing a traceback.

Show the traceback line numbers as well as the current line numbers if an exception is being debugged.  Courtesy of pdb++ by Antonio Cuni.  Also document -> and >> markers for "list".

* added basic test for basic commands
* removed duplication of command docs, and moved them to their implementation
* unified and useful display of exceptions
* output messages and errors using overridable methods (also fixes #1503502)

Add Breakpoint.bpformat(), which returns the info usually printed by bpprint().  Necessary for major refactoring of pdb output handling.

#809887: improve pdb feedback for breakpoint-related actions.  Also add a functional test for these commands.

#6719: In pdb, do not stop somewhere in the encodings machinery if the source file to be debugged is in a non-builtin encoding.