Plan for changing the binary toolchain to 4.7 and hardfloat

[Michael Hope]

Hi there.  Over the next three months both GCC 4.7 and Ubuntu 12.04
'Precise' are coming out.  We'll switch over to these pretty quickly
which will affect our internal testing and anyone using the binary
toolchain.

The changeover plan including dates, details of what's happening, and
backwards compatibility is at:
 https://wiki.linaro.org/MichaelHope/Sandbox/BinariesMigration

Comments and concerns are welcome,

-- Michael