Use size_t, not int, for byte counts.

Derived from #37.

lib/tre-match-parallel.c

@@ -152,7 +152,7 @@ tre_tnfa_run_parallel(const tre_tnfa_t *tnfa, const void *string, int len,
      everything in a single large block from the stack frame using alloca()
      or with malloc() if alloca is unavailable. */
   {
-    int tbytes, rbytes, pbytes, xbytes, total_bytes;
+    size_t tbytes, rbytes, pbytes, xbytes, total_bytes;
     char *tmp_buf;
     /* Compute the length of the block we need. */
     tbytes = sizeof(*tmp_tags) * num_tags;
@@ -167,11 +167,11 @@ tre_tnfa_run_parallel(const tre_tnfa_t *tnfa, const void *string, int len,
 #ifdef TRE_USE_ALLOCA
     buf = alloca(total_bytes);
 #else /* !TRE_USE_ALLOCA */
-    buf = xmalloc((unsigned)total_bytes);
+    buf = xmalloc(total_bytes);
 #endif /* !TRE_USE_ALLOCA */
     if (buf == NULL)
       return REG_ESPACE;
-    memset(buf, 0, (size_t)total_bytes);
+    memset(buf, 0, total_bytes);
 
     /* Get the various pointers within tmp_buf (properly aligned). */
     tmp_tags = (void *)buf;