virt-resize: Be much more conservative about moving first partition.

Commit 2910413850c7d9e8df753afad179e415f0638d6d caused Windows 7
resizes to break with the 0xc0000225 boot error.

Change the --align-first auto (default) option so that it is more
conservative about when it moves the first partition.  In particular
it doesn't move it if it's already aligned (as it is for Win7), nor if
there is more than one partition (also Win7).

Tested with: Windows XP, 2003, 7, Ubuntu 10.10 and RHEL 5.