for backward compatible
remove redundant file
Revert "remove redundant file"

This reverts commit c99a9a422812441ef452e7396d99eadb47724fcd.
Thread uniqueness check was removed from spin lock.
Locked and tail check were changed.
Locked and tail check were changed.
fixed issue #3051
fixed regression on function execution, introduced with last optimization (script engine pooling): a function could not be executed twice, second time it threw an exception
Merge branch 'develop' of https://github.com/orientechnologies/orientdb into develop
Fixed issue #3106 allowing to get TX changes by external listeners
Minor: Skipped hidden files in plugin loading
Tests: fixed problem on run single tests with memory database
Merge branch 'develop' of https://github.com/orientechnologies/orientdb into develop

Conflicts:

core/src/main/java/com/orientechnologies/orient/core/db/record/OClassTri
gger.java
Waiting readers are cleared during release.
Issue #3094 was fixed.
Merge branch 'develop' of github.com:orientechnologies/orientdb into develop
Minor: improved JSON manipulation
Fixed issue on cleaning record tracking after delete
Issue #3089 was fixed.
fixed #3103