Flip binary32 and binary64 so it matches output options

[mandli]

Addresses clawpack/geoclaw#656

[rjleveque]

It used to be that file_format = "binary" meant binary64, but now it means binary32 with the new

    format_map = {'ascii':1, 'binary':2, 'binary32':2, 'binary64':3}

It seems like the default should be full precision? That would be consistent with the convention used for fort files in /Users/rjl/git/clawpack/pyclaw/src/pyclaw/fileio/binary.py and also the convention used for fgout grids.
So I suggest changing this to

    format_map = {'ascii':1, 'binary':3, 'binary32':2, 'binary64':3}

[mandli]

Yeah, that sounds right to me, thanks for catching that.

[rjleveque]

Thanks @mandli, I'll work on the release later today.