Use pkg-config Autoconf check for libparted version first (#740004)

Currently ./configure links and runs a program to query the libparted
library version, which is used to determine the availability of some
features.  This makes cross-compiling harder because the compile host
has to fake a virtual installation target in which to run the check.
Because of this, pkg-config based Autoconf checks are preferred.

Switch to using a pkg-config based Autoconf check first to determine the
version of libparted, falling back to the previous method for older
distributions which don't provide a pkg-config file for libparted.

Also small comment tidy-up elsewhere.

Bug 740004 - use pkg-config to check for version of libparted