Adapted RESTXQ to stack-frames.
[MOD] All Expr instances are now either abstract or final.
Merge pull request #69 from LeoWoerteler/stack-frames

[MOD] All Expr instances are now either abstract or final.
[MOD] Synchronized with master commits
Merge branch 'master' into stack-frames

Conflicts:
	src/main/java/org/basex/http/restxq/RestXqModule.java
Merge pull request #71 from BaseXdb/stack-frames

Changes triggered by those in the main repo.