Plasma manager performance: speed up wait with a wait request object map (#427)

* plasma manager perf: speedup wait with a wait request object map

* removing duplicate == operator in plasma store

* fix serialization test

* code cleanup

* minor cleanup

* factoring out uniqueid hash and equality operators into common

* plasma manager: c++ify the WaitRequest struct

* plasma manager: get rid of the initial object request malloc

* cleanup

* linting

* cleanups and fix compiler warnings

* compiler warnings and linting

src/common/common.cc

@@ -7,6 +7,7 @@
 #include <fcntl.h>
 
 #include "io.h"
+#include <functional>
 
 /* This is used to define the array of object IDs. */
 const UT_icd object_id_icd = {sizeof(ObjectID), NULL, NULL, NULL};
@@ -29,6 +30,11 @@ UniqueID globally_unique_id(void) {
   return result;
 }
 
+/* ObjectID equality function. */
+bool operator==(const ObjectID &x, const ObjectID &y) {
+  return UNIQUE_ID_EQ(x, y);
+}
+
 bool ObjectID_equal(ObjectID first_id, ObjectID second_id) {
   return UNIQUE_ID_EQ(first_id, second_id);
 }