Fix typos in /Documentation : 'U-Z'

This patch fixes typos in various Documentation txts. The patch addresses some
+words starting with the letters 'U-Z'.

Looks like I made it through the alphabet...just in time to start over again
+too!  Maybe I can fit more profound fixes into the next round...?  Time will
+tell. :)

Signed-off-by: Matt LaPlante <[email protected]>
Acked-by: Randy Dunlap <[email protected]>
Signed-off-by: Adrian Bunk <[email protected]>

Documentation/block/biodoc.txt

@@ -391,7 +391,7 @@ forced such requests to be broken up into small chunks before being passed
 on to the generic block layer, only to be merged by the i/o scheduler
 when the underlying device was capable of handling the i/o in one shot.
 Also, using the buffer head as an i/o structure for i/os that didn't originate
-from the buffer cache unecessarily added to the weight of the descriptors
+from the buffer cache unnecessarily added to the weight of the descriptors
 which were generated for each such chunk.
 
 The following were some of the goals and expectations considered in the
@@ -403,14 +403,14 @@ i.  Should be appropriate as a descriptor for both raw and buffered i/o  -
     for raw i/o.
 ii. Ability to represent high-memory buffers (which do not have a virtual
     address mapping in kernel address space).
-iii.Ability to represent large i/os w/o unecessarily breaking them up (i.e
+iii.Ability to represent large i/os w/o unnecessarily breaking them up (i.e
     greater than PAGE_SIZE chunks in one shot)
 iv. At the same time, ability to retain independent identity of i/os from
     different sources or i/o units requiring individual completion (e.g. for
     latency reasons)
 v.  Ability to represent an i/o involving multiple physical memory segments
     (including non-page aligned page fragments, as specified via readv/writev)
-    without unecessarily breaking it up, if the underlying device is capable of
+    without unnecessarily breaking it up, if the underlying device is capable of
     handling it.
 vi. Preferably should be based on a memory descriptor structure that can be
     passed around different types of subsystems or layers, maybe even