Slight update to User Defined Roles description

Make it clear that the system.users collection lives in the "admin" database, not in arbitrary databases as was true in v2.4.

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

Changed 'including vitalized instances' to 'including virtualized instances'

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-1199: making correction regarding dump/restore compatibility issue with 2.2
DOCS-1563 adding note about background index construction on secondaries
DOCS-739: finalizing text for noIndexBuildRetry
DOCS-1926: Master/slave treats w:majority as w:1

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-1980, DOCS-1934, DOCS-1935, DOCS-1936: new user and role features