Build: avoid win32-incompatible functions

[GBillotey]

Dating from commit e1e0848, I have been experimenting compiling errors (under win32).

c:\users\geoffroy\documents\github\matplotlib\src\path_converters.h(895) : error C3861: 'seed48': identifier not found
        c:\users\geoffroy\documents\github\matplotlib\src\path_converters.h(893) : while compiling class template member function 'void Sketch<VertexSource>::rewind(unsigned int)'
        with
        [
            VertexSource=curve_t
        ]
        src/_path.cpp(1516) : see reference to class template instantiation 'Sketch<VertexSource>' being compiled
        with
        [
            VertexSource=curve_t
        ]

They seem to be linked with the use of traditional UNIX functions like drand48 in path_converters.h. seed48 and M_PI are also problematic.

Enclosed is a patch attempt which uses ANSI C function rand and srand instead, and at least compile correctly - with win SDK. (The code being quite complex I can't be sure with my limited C++ knowledge this is the best way to deal with it ; hope it can help though)

[mdboom]

Indeed. I should have been more careful about sticking to ANSI C. Thanks for the PR.

[GBillotey]

Thanks for the merge.

While having a last read:
shouldn't I have used doubles instead of floats for _drand and _M_PI ? If you confirm, I would be happy to do the short corrective PR (sorry, I should have paid more attention in the first place).

[mdboom]

Indeed. Thanks for catching that. Practically speaking, I don't think it much matters on images of reasonably normal size. However, we should probably be consistent with doubles everywhere (since that's what's used for vertices in general).