[PATCH] Fix typos in comments, NFC

[JF Bastien]

Looks good save for one place. Feel free to fix and commit.

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Comment at: include/llvm/CodeGen/MachinePostDominators.h:25
@@ -24,3 +24,3 @@
 /// PostDominatorTree Class - Concrete subclass of DominatorTree that is used
-/// to compute the a post-dominator tree.
+/// to compute the ``post-dominator tree.
 ///
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?

http://reviews.llvm.org/D5130