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'

The attached patch solves this 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.

Is someone willing to eyeball this one before I
check it in? Thanks.