Put acorn parse in synchronized block
Put acorn parse in synchronized block

This change puts the call to Acorn parse() within a synchronized block,
in order to prevent a problem (Nashorn bug?) with it otherwise
apparently not being safe across threads.

takenspc/validator,validator/validator,takenspc/validator,validator/validator,validator/validator,takenspc/validator,validator/validator,takenspc/validator,validator/validator,takenspc/validator