Fixed MSVC11 amd64 builds.

Visual Studio Express 2012 only installs the cross-compiler
tool (%VSINTALLDIR%/VC/bin/x86_amd64 directory) for amd64.
This commit checks for the amd64 directory first, and falls
back to x86_64.
Moved regenerate_build() to pynja module.
Propagated warn/error logs, got win8 sdk working.

Now if a compile/lib/link invocation's log contains the words
"error" or "warning", the log is printed to the output.
This is now decoupled from the invocation's exit code, so that
warnings will always be displayed.

Added path calculations for win8 sdk, which rearranges everything.