Fix typos in documentation.

docs/ispc.txt

@@ -1833,7 +1833,10 @@ One thing to note is that that the value being added to here is a
 ``uniform`` integer, while the increment amount and the return value are
 ``varying``.  In other words, the semantics are that each running program
 instance individually issues the atomic operation with its own ``delta``
-value and gets the previous value of ``val`` back in return.
+value and gets the previous value of ``val`` back in return.  The atomics
+for the running program instances may be issued in arbitrary order; it's
+not guaranteed that they will be issued in ``programIndex`` order, for
+example.
 
 Here are the declarations of the ``int32`` variants of these functions.
 There are also ``int64`` equivalents as well as variants that take
@@ -1865,7 +1868,7 @@ compares the value in "val" to "compare"--if they match, it assigns
 into the code; it ensures that all memory reads and writes prior to be
 barrier complete before any reads or writes after the barrier are issued.
 See the `Linux kernel documentation on memory barriers`_ for an excellent
-writeup on the need for that the use of memory barriers in multi-threaded
+writeup on the need for and the use of memory barriers in multi-threaded
 code.
 
 .. _Linux kernel documentation on memory barriers: http://www.kernel.org/doc/Documentation/memory-barriers.txt