Updates to movePrimary command page

The conditions when it is safe to call movePrimary need to be tighter than mentioned, and we should mention that the other mongos do not know about the change until restarted/flushRouterConfig'ed.

Signed-off-by: Sam Kleinman <samk@10gen.com>
Update movePrimary.txt

Updated the patch and added the last two sentences to warn about potentially missing data.

Signed-off-by: Sam Kleinman <samk@10gen.com>
Update movePrimary.txt

Another tweak, grammar-stuff.

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3214: clarification and style