Greasemonkey 4.13 release

The entire list of bugs handled in this release is also available via the 4.13 milestone on GitHub. If you are using this version and notice problems, it's best to let us know at greasemonkey-users (and be clear that it's with this version).

New features:

• GM.openInTab() now works in Firefox for Android. (#3189)

Fixed bugs:

• Importing a backup could fail when "overwrite already installed scripts" (enabled by default) was disabled. (#3195)
• Previously unreliable automatic script updates should now work as intended. (#3190)