Use relative import

This way the import statements remain the same in both Blender's
io_blend_utils module and BAM.

io_blend_utils/blend/blendfile_path_walker.py

@@ -395,7 +395,7 @@ def iter_blocks_idlib():
  # store info to pass along with each iteration
  extra_info = rootdir, os.path.basename(filepath)
 
- from blend import blendfile
+ from . import blendfile
  with blendfile.open_blend(filepath_tmp, "rb" if readonly else "r+b") as blend:
 
  for code in blend.code_index.keys():
@@ -627,7 +627,7 @@ def iter_ListBase(block, next_item=b'next'):
 
  def iter_array(block, length=-1):
  assert(block.code == b'DATA')
- from blend import blendfile
+ from . import blendfile
  import os
  handle = block.file.handle
  header = block.file.header