names for temporary files and folders generated by weave are too large for MSVC

[bbudescu]

MSVC has a max length of 260 chars for input/output paths, which is exceeded when using weave. A possible solution (which I tested and seems to work) is to modify the unique name generation algorithm by making it use md5 hex checksums instead of sha256 (which are 64 characters long). The places where I made the modifications are in catalog.expr_to_filename (https://github.com/scipy/scipy/blob/master/scipy/weave/catalog.py#L93) and platform_info.check_sum (https://github.com/scipy/scipy/blob/master/scipy/weave/platform_info.py#L99). This is also caused by the fact that the path to the output obj also replicates the whole path of the cpp.

[rgommers]

This is a duplicate of gh-3216. I actually plan to fix that today and then release 0.13.3 asap.

Thanks for the suggested fixes.

[rgommers]

Fix submitted: gh-3232.