Fix the do_generic_file_read()-reads-one-page-too-many-bug for the fifth
time.

This patch combines the best features from Nick's patch and also makes
index and end_index consistent.  (i.e index 'n' covers n*PAGE_SIZE to
((n+1)PAGE_SIZE)-1.  I did not feel comfortable with the way index and
end_index represented different ranges.  It was like comparing apples with
oranges.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>