Add instruction alignment tests to unit tests.

src/PNaClTranslator.cpp

Index: src/PNaClTranslator.cpp
diff --git a/src/PNaClTranslator.cpp b/src/PNaClTranslator.cpp
index 482844f56412748855ad9f4ca8a7d08765fffe37..9258f67f3cd3b7234429d9f8dbea3db34c79b3cd 100644
--- a/src/PNaClTranslator.cpp
+++ b/src/PNaClTranslator.cpp
@@ -1174,11 +1174,11 @@ private:
   }
 
   // Extracts the corresponding Alignment to use, given the AlignPower
-  // (i.e. 2**AlignPower, or 0 if AlignPower == 0). InstName is the
+  // (i.e. 2**(AlignPower-1), or 0 if AlignPower == 0). InstName is the
   // name of the instruction the alignment appears in.
   void extractAlignment(const char *InstName, uint32_t AlignPower,
                         uint32_t &Alignment) {
-    if (AlignPower <= AlignPowerLimit) {
+    if (AlignPower <= AlignPowerLimit + 1) {
       Alignment = (1 << AlignPower) >> 1;
       return;
     }