Merge branch '3749_vfs_blksize'

Merge branch '3749_vfs_blksize'

* 3749_vfs_blksize:
  (vfs_adjust_stat): new VFS API, currently used to calculate st_blocks.
  Clarify usage of st_rdev. Use it if HAVE_STRUCT_STAT_ST_RDEV is defined.
  ftpfs: define st_blksize as equal to 64K.
  fishfs: define st_blksize as equal to 64K.
  Modify VFS APIs.
  tarfs: define st_blksize as equal to 8K.
  sftpfs: (sftpfs_fix_filename): refactoring: return length of result.
  sftpfs: minor optimization.
  sftpfs: define st_blksize and st_blocks.
  (vfs_s_default_stat): define st_blksize and st_blocks explicitly.
  Clarify usage of st_blocks. Use it if HAVE_STRUCT_STAT_ST_BLOCKS is defined.
  Ticket #3749: fix segfault in VFS if block size is not set.