This is a complete implementation of PEP-328, relative imports, 
including the future statement to enable absolute imports by default. 
It's currently lacking tests and documentation. A couple of caveats:

 - It's implemented by extending the stack-arguments of the 
IMPORT_NAME opcode, but it doesn't up the bytecode magic. You need 
to 'make clean' or 'make distclean' to remove existing .pyc/.pyo files, 
or you'll get random crashes.

 - It's implemented by adding a 5th (optional) argument to __import__, 
to the end, for 'relative depth'. This new argument, 'lvl', can be -1, 0 or 
a positive number. -1 signals 'non-absolute non-dotted import', or 
exactly the same as 'import module' before. 0 signals 'absolute non-
dotted import', which means 'import module' with absolute-imports 
enabled (by using 'from __future__ import absolute_import'.) A positive 
number is the number of dots in 'import ...module'; the amount of 
relativeness of the import.

 - __import__'s 5th value defaults to -1 for now. It should obviously 
change to 0 when absolute imports are the absolute truth (in 2.7 or 
so.)

 - The 5th argument to __import__ is only passed when it's not -1, so 
'old' __import__ replacements still work as long as code doesn't use 
'import ..module' or 'from __future__ import absolute_import'.

 - I haven't tested it extensively with frozen or zipped modules or 
custom importhooks and what not. The testsuite shows no failures for 
me (on MacOS and Linux) but none of the test modules use 
'import ..test' or 'from __future__ import absolute_import'.

This patch was brought to you by Lufthansa "babycarrier" Airlines and 
10 hours stuffed in a too small chair surrounded by crying, whiney 
babies and kids.

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I just noticed I didn't quite implement the right thing. 'from ..module import 
something' works as expected, but 'from . import module' is not implemented, 
and the 'import .module' syntax Guido rejected actually *is* implemented. I 
guess I'll have to fix that ;)

On the upside, it seems this patch Just Works(tm) with zipimports, so I have 
reasonable faith that it's going to work across the board.

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A slightly modified patch that implements all of PEP-328 correctly. It does so by, 
at AST-generation time, changing 'from . import module' into 'import .module', 
and disallowing 'module .module' directly. I'm not sure if the AST should do that 
or not, but that's the easiest way to add it.

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And now a full, proper, complete implementation, with tests and everything. It 
should be just about done, barring small bugfixes, documentation, and 
parsermodule and compilerpackage support.

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Thomas checked this in.