[lvm-devel] Remove NONBLOCK flag from higher-level tools.

[Dave Wysochanski]

The following two patches are two approaches to solving the
same problem: remove the NONBLOCK flag from the higher-level
vg_read() function.  This simplifies the API for the user.

Both patches take a similar approach - enforce a policy that
the second VG lock implicitly sets the NONBLOCK flag.  One
patch places the code inside lock_vol() and should apply
cleanly on upstream LVM.  The other patch places the code
inside the new vg_read() interface and should apply cleanly
on top of Petr's vg_read() patches submitted on May 3.