Update source/faq/concurrency.txt

Simple typo - word missing in the JS operations paragraph
SERVER-7994: clarifying that timeLockedMicros may be longer than total operation length.
SERVER-7994: updating timeLockedMicros
merge: minor fix
DOCS-924: clarifiy connection pooling faq
DOCS-924 adding ulimit and rewording question
geospatial indexes review edits
DOCS-853 toArray method
DOCS-957: clarification behavior on upserts that turn into inserts
Update source/release-notes/2.4.txt

added note about $intersects becoming $geoIntersects
Correct wikipedia link re: sparse index
DOCS-853 shorten sentences and change variable name
DOCS-853 shorten sentences and change variable name
DOCS-957: clarification based on comments from @TylerBrock
merge: DOCS-583
DOCS-853 use the ~ expression
merge: DOCS-853
merge: link change
migration: adding link target
theme: cleanup unused macros fixing header.