Performance tweaks for curl_multi

* Avoid massive slowdown due to persistent connection handling
* Avoid extra usleep() call on each request set

Change-Id: I3573dd8212d19e3bfebeb5a7f1a5d2425ebd4426
Update documentation

Change-Id: Idf4af357983d9376ae8692cecf992a4aa1c768a4
Localisation updates from https://translatewiki.net.

Change-Id: I2e1293e7cd1ea20fbd2b7554d0cb673e1f7728f7
Localisation updates from https://translatewiki.net.

Change-Id: I09dc74655a3947a67631b25723d51fcaab364987
Migrate to JSON i18n

Procedure per https://www.mediawiki.org/wiki/Manual:GenerateJsonI18n.php
with shim.

Change-Id: I9d16c7e9d199bfc1b425891e5824e0d814b270fd
Fix spelling: 'occurred'

Change-Id: Icfb5cbfa935a3abb46db186106762a162ada0966