Documentation: remove duplicated words

Remove many duplicated words under Documentation/ and do other small
cleanups.

Examples:
        "and and" --> "and"
        "in in" --> "in"
        "the the" --> "the"
        "the the" --> "to the"
        ...

Signed-off-by: Paolo Ornati <ornati@fastwebnet.it>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
diff --git a/Documentation/networking/decnet.txt b/Documentation/networking/decnet.txt
index e6c39c5..badb748 100644
--- a/Documentation/networking/decnet.txt
+++ b/Documentation/networking/decnet.txt
@@ -82,7 +82,7 @@
 address of the node in order for it to be autoconfigured (and then appear in
 /proc/net/decnet_dev). There is a utility available at the above
 FTP sites called dn2ethaddr which can compute the correct ethernet
-address to use. The address can be set by ifconfig either before at
+address to use. The address can be set by ifconfig either before or
 at the time the device is brought up. If you are using RedHat you can
 add the line: