Remove structural records from libcore, libstd, macros

[catamorphism]

libcore has structural records removed for the most part (thanks to @erickt 's heroic work!) but a few modules still have it enabled because the pipes code generates code with structural records. I'm a little afraid to fix the pipes compiler (I'm not sure how to make it generate new names for struct types), but could with some help.

The extfmt code also needs to be changed to not generate structural records.

Finally (for now), libstd needs to have records removed as well.

[erickt]

I already landed my extfmt and pipes patches, and most of libstd has been converted too. I'm just waiting on a snapshot to remove my #[cfg(stage...)] blocks.

[catamorphism]

@erickt Great, thanks! Sorry, I must have read your patches hastily and didn't notice that you also fixed extfmt and pipes :-)

[catamorphism]

I have a new snapshot ready that should work for this; currently running try.

[catamorphism]

I've de-recorded libstd and am just running tests. I also have a snapshot branch that should build, but is not compiling on the Mac and Linux bots (I'm investigating).

[catamorphism]

I forgot to remove one use of structural records from the pipes compiler ( gen_buffer_init in libsyntax/ext/pipec.rs). >:-(

[catamorphism]

I'll try to finish this now that df4273f is in. Specifically I'll start a snapshot building.

[catamorphism]

Snapshot is now building.

[bstrie]

I think this can be closed now.