Merge pull request #180 from spneto/patch-1

Dropping FK before UK to avoid MySQL error 150

modules/activiti-engine/src/main/resources/org/activiti/db/upgrade/activiti.mysql.upgradestep.514.to.515.engine.sql

 alter table ACT_RU_TASK 
     add CATEGORY_ varchar(255);
     
-alter table ACT_RU_EXECUTION drop index ACT_UNIQ_RU_BUS_KEY;    
+alter table ACT_RU_EXECUTION drop foreign key ACT_FK_EXE_PROCDEF;  	
+
+alter table ACT_RU_EXECUTION drop index ACT_UNIQ_RU_BUS_KEY;  
+
+alter table ACT_RU_EXECUTION
+    add constraint ACT_FK_EXE_PROCDEF 
+    foreign key (PROC_DEF_ID_) 
+    references ACT_RE_PROCDEF (ID_);
 
 update ACT_GE_PROPERTY set VALUE_ = '5.15-SNAPSHOT' where NAME_ = 'schema.version';