Take file size using fstat in map_in_file() in umap_file.hpp

[KIwabuchi]

In map_in_file(), I think, we can take the file size using fstat instead of using the 'numbytes' argument when either initonly or !noinit is true.
Consequently, the code below won't be necessary.
if ( (off_t)sbuf.st_size != (numbytes) ) { std::cerr << filename << " size " << sbuf.st_size << " does not match specified data size of " << (numbytes) << std::endl; return NULL; }

What do you think?

[KIwabuchi]

@mcfadden8 what do you think? This is a reason why we had to change the input value (#of edges) to run the old BFS program.

[mcfadden8]

It seems reasonable, but I'm not really sure. It might be best to get @egreen77 involved as I don't know whether I will be able to look at it any time soon.