Update from 1.4.25 to 1.4.27.

<ChangeLog>

This is a maintenance release for version 1.4.
Update urgency: Medium

Headlines:

This release improves overall stability and provides fixes for
issues found after the previous release.

Features:

• Added exists function that can be used on conditional updates (REPLACE PARTIAL) to check if a field exists in the document.

Minor Enhancements:

• Lazy evaluation of the right side of 'or'/'and' clauses in IF condition.

Bugfixes:

• Rare GC failure when accessing uninitialized variable.
• Crash on highlighting a search query where the document no longer exists.

Note: we skipped 1.4.26 for technical reasons.

</ChangeLog>