branches/zip: Restore the size of row_merge_block_t to 1048576 bytes.

This was inadvertently reduced to 16384 bytes in r1861.  For testing,
this can be set as low as UNIV_PAGE_SIZE.

row/row0merge.c

@@ -48,7 +48,7 @@ static ibool	row_merge_print_write;
 
 /* Block size for I/O operations in merge sort */
 
-typedef byte	row_merge_block_t[16384];
+typedef byte	row_merge_block_t[1048576];
 
 /* Secondary buffer for I/O operations of merge records */