linux: use libblkid to determine ->phys_sector_size

linux: use libblkid to determine ->phys_sector_size

Before this change, creating a memory-mapped disk on a fedora-based
system running 2.6.31.1-56.fc12.x86_64 using this command:
modprobe scsi_debug dev_size_mb=1025 sector_size=4096
and then running "parted -s /dev/sdd mklabel gpt print"
would mistakenly print "Sector size (logical/physical): 4096B/512B"
The "512B" is what's wrong.  It should be "4096B".
* configure.ac: Test for a new-enough blkid library.
* libparted/Makefile.am (libparted_la_LIBADD): Add $(LIB_BLKID).
* libparted/arch/linux.c (get_minimum_io_size): New function.
(_device_set_sector_size): Use it.