Automatically enable online resize with libparted >= 3.2 (#734076)

Configure script checks for libparted version >= 3.2 to automatically
determine the availability of online resize capability in libparted.
This can be overridden from the ./configure command line.  Override
enable when an older version of libparted has been patched to include
online resize support with:

    ./configure --enable-online-resize

Override disable with libparted 3.2 or later to disable the feature when
it is not wanted with:

    ./configure --disable-online-resize

Note that GParted also requires, and checks for at runtime, Linux
kernel >= 3.6 for online resize support.  See commit for more details:

    de2844d02df02ad6ccf0f2caf7f63622cf4d25de
    Add online resize support (#694622)

Bug #734076 - Autodetect parted online partition resizing capability
Tidy up Autoconf check for --enable-libparted-dmraid (#734076)

Use AC_ARG_ENABLE() Autoconf macro to set enable_libparted_dmraid
variable to either yes or no in all cases, whether set on the command
line or not.  Use AS_HELP_STRING() macro to format the option help text.

Bug #734076 - Autodetect parted online partition resizing capability
Tidyup Autoconf check for --disable-doc (#734076)

Use AC_ARG_ENABLE() and AS_HELP_STRING() macros to improve handling of
the --disable-doc option.

Change the names, and sence, of the Autoconf and Automake definitions
used to control building of the help documentation.  Reasons are:
(1) Switch from negative to positive statements which are more natural
    to comprehend.
(2) Insert HELP in the names from *_DOC to *_HELP_DOC as they control
    building of the documentation in the help subdirectory, not the
    manual page in the doc directory.

Autoconf: HAVE_DISABLE_DOC -> ENABLE_HELP_DOC
Automake: DISABLE_DOC      -> BUILD_HELP_DOC

Bug #734076 - Autodetect parted online partition resizing capability