Upgrade gitian win32 to Precise 12.04.

mingw upgrade allows more hardening, compiler bug fixes and possibily win64 later.
Rename deps .zip files to be more consistent in revision format.
Boost #4258 build fix for mingw32
Upgrade gitian win32 to boost-1.54.0

Workaround 1.54.0 build bug, upstream #9156
Workaround 1.51.0+ human bug, upstream #7262

This commit also demonstrates a method to verify the integrity of inputs.