windows compile + optional alternate magic header

[graehl]

windows compile (MSVC2010) - std::min, WINBOOL typedef was needed for my compile on Visual Studio 2010

SetAlternateMagicBeforeVersion allows a second, customizable file header. I've been maintaining it locally and it would be nice to have it included in kpu:master (nice for me, at least).

[kpu]

Kareem M. Darwish (kdarwish at qf.org.qa) encountered the OS X issue and reported that this fixed it on 3/31/2013. I don't have a Mac, so it's hard for me to retest these things.

I'm working on ACL short and hope you can wait until after the deadline. . . unsure I can endorse DRM though.

[kpu]

I cherry-picked the std::min change in 032e60a and the WINBOOL typedef in an64cdb2220e251df3d2cd4c0b5fc58d77ed964708d . Hope it works on Windows now.

Here's a one-line change to allow both 'encrypted' and 'unenecrypted' formats to load. In binary_format.cc, change
if (!std::memcmp(memory.get(), &reference_header, sizeof(Sanity))) return true;
to
if (!std::memcmp((uint8_t*)memory.get() + strlen(kMagicBeforeVersion), &reference_header + strlen(kMagicBeforeVersion), sizeof(Sanity) - strlen(kMagicBeforeVersion))) return true;

It will lose some error handling, like detecting incomplete files quickly. But it still has a low collision probability due to the other magic bytes for endianness testing and will allow anybody to load LMs distributed by SDL/LW regardless of the magic bytes you use.