Avoid unaligned loads in stringtable.c hash function

On some architectures unaligned loads may not work at all,
e.g. older ARM CPUs return corrupted data on unaligned loads.

src/root/stringtable.c

@@ -21,6 +21,13 @@ hash_t calcHash(const char *str, size_t len)
 {
     hash_t hash = 0;
 
+    union
+    {
+        uint8_t  scratchB[4];
+        uint16_t scratchS[2];
+        uint32_t scratchI;
+    };
+
     while (1)
     {
         switch (len)
@@ -35,18 +42,26 @@ hash_t calcHash(const char *str, size_t len)
 
             case 2:
                 hash *= 37;
-                hash += *(const uint16_t *)str;
+                scratchB[0] = str[0];
+                scratchB[1] = str[1];
+                hash += scratchS[0];
                 return hash;
 
             case 3:
                 hash *= 37;
-                hash += (*(const uint16_t *)str << 8) +
+                scratchB[0] = str[0];
+                scratchB[1] = str[1];
+                hash += (scratchS[0] << 8) +
                         ((const uint8_t *)str)[2];
                 return hash;
 
             default:
                 hash *= 37;
-                hash += *(const uint32_t *)str;
+                scratchB[0] = str[0];
+                scratchB[1] = str[1];
+                scratchB[2] = str[2];
+                scratchB[3] = str[3];
+                hash += scratchI;
                 str += 4;
                 len -= 4;
                 break;