This patch speeds up copy_*_user for some Intel ia32 processors.  It is
based on work by Mala Anand.

It is a good win.  Around 30% for all src/dest alignments except 32/32.

In this test a fully-cached one gigabyte file was read into an
8192-byte userspace buffer using read(fd, buf, 8192).  The alignment of
the user-side buffer was altered between runs.  This is a PIII.  Times
are in seconds.

User buffer	2.5.41		2.5.41+
				patch++

0x804c000	4.373		4.343
0x804c001	10.024		6.401
0x804c002	10.002		6.347
0x804c003	10.013		6.328
0x804c004	10.105		6.273
0x804c005	10.184		6.323
0x804c006	10.179		6.322
0x804c007	10.185		6.319
0x804c008	9.725		6.347
0x804c009	9.780		6.275
0x804c00a	9.779		6.355
0x804c00b	9.778		6.350
0x804c00c	9.723		6.351
0x804c00d	9.790		6.307
0x804c00e	9.790		6.289
0x804c00f	9.785		6.294
0x804c010	9.727		6.277
0x804c011	9.779		6.251
0x804c012	9.783		6.246
0x804c013	9.786		6.245
0x804c014	9.772		6.063
0x804c015	9.919		6.237
0x804c016	9.920		6.234
0x804c017	9.918		6.237
0x804c018	9.846		6.372
0x804c019	10.060		6.294
0x804c01a	10.049		6.328
0x804c01b	10.041		6.337
0x804c01c	9.931		6.347
0x804c01d	10.013		6.273
0x804c01e	10.020		6.346
0x804c01f	10.016		6.356
0x804c020	4.442		4.366

So `rep;movsl' is slower at all non-cache-aligned offsets.

PII is using the PIII alignment.  I don't have a PII any more, but I do
recall that it demonstrated the same behaviour as the PIII.

The patch contains an enhancement (based on careful testing) from
Hirokazu Takahashi <taka@valinux.co.jp>.  In cases where source and
dest have the same alignment, but that aligment is poor, we do a short
copy of a few bytes to bring the two pointers onto a favourable
boundary and then do the big copy.

And also a bugfix from Hirokazu Takahashi.

As an added bonus, this patch decreases the kernel text by 28 kbytes.
22k of this in in .text and the rest in __ex_table.  I'm not really
sure why .text shrunk so much.

These copy routines have no special-case for constant-sized copies.  So
a lot of uaccess.h becomes dead code with this patch.  The next patch
which uninlines the copy_*_user functions cleans all that up and saves
an additional 5k.