[Trivial] Grammar and typo correction

Minor corrections in src\test\* .

src/test/scheduler_tests.cpp

@@ -47,8 +47,8 @@ BOOST_AUTO_TEST_CASE(manythreads)
     //
     // So... ten shared counters, which if all the tasks execute
     // properly will sum to the number of tasks done.
-    // Each task adds or subtracts from one of the counters a
-    // random amount, and then schedules another task 0-1000
+    // Each task adds or subtracts a random amount from one of the
+    // counters, and then schedules another task 0-1000
     // microseconds in the future to subtract or add from
     // the counter -random_amount+1, so in the end the shared
     // counters should sum to the number of initial tasks performed.