test_largefile can leave its temp file open if one of many tests fail. On

test_largefile can leave its temp file open if one of many tests fail. On
platforms (e.g., Cygwin) that are "particular" about open files, this will
cause other regression tests that use the same temp file to fail:

    $ ./python.exe -E -tt Lib/test/regrtest.py -l
    test_largefile test_mmap test_mutants
    test_largefile
    test test_largefile failed -- got -1794967295L, but expected 2500000001L
    test_mmap
    test test_mmap crashed -- exceptions.IOError: [Errno 13] Permission denied: '@test'
    test_mutants
    test test_mutants crashed -- exceptions.IOError: [Errno 13] Permission denied: '@test'

This patch solves the problem by adding missing "try/finally" blocks. Note
that the "large" size of this patch is due to many white space changes --
otherwise, the patch is small.

I tested this patch under Red Hat Linux 8.0 too.