More hardening with gitian win32, upgrade to Precise 12.04.

mingw upgrade enables more hardening, fixes many bugs and possibily win64 later.
Rename deps .zip files to be more consistent in revision format.
Remove "msvc" compat triplet name.
Upgrade win32 gitian to boost-1.54.0.

Boost Workarounds
=================
Workaround 1.54.0  build bug, upstream #9156
Workaround 1.54.0  build bug, binary-format=pe
Workaround 1.51.0+ human bug, upstream dev refuses to include patch to allow cross-compile.