Slightly improved performance by reading the current version number directly from the plugin file instead of asking WordPress to fetch all installed plugins. The version number is cached for the current page load. 

Caution: There might be some issues in how/when the cache is cleared. It looks fine in theory, but I may have missed something (bulk upgrades? Multisite side-effects?).

Also removed two unused parameters from addCheckForUpdatesLink(). We can always add them back later if needed.

Version bump: 1.3.2