man: document DM_DEFAULT_NAME_MANGLING_MODE

Document DM_DEFAULT_NAME_MANGLING_MODE environmental variable.
(its default setting is build time configurable)
configure: accept 'none' as mangling mode

Since we advertise 'none' as mangling name, accept it.
Keep it backward compatible and leave disabled option still working
(though I guess there is likely no user of this option...)
configure: cleanups

Replace AC_PATH_PROG with AC_PATH_TOOL.
Drop 'x' when already using "" around shell variable.
Simlify some long line and ifs.
Merge multiple test evaluation with '-a', '-o'.
Use 'case' instead if several ifs when it's more elegant.
Improve usage of pkg_config_init and add it where it's been missing.
Check for UDEV_HAS_BUILTIN_BLKID and when building udev-rules.
configure: reconfigure
tests: fix use of double apostrophes in get

Need to put "" around parameters.
tests: use shell arrays to keep device names

Better preserving spaces in device path name,
though admitely rest of test suite need
more repairs...
tests: add get_devs function

Instead of rereading device list via cat - keep
the list in bash array. (Also solves problem
with spaces in device path)

Move usage of  "$path" out of lvm shell usage,
since we don't support such thing there...
tests: use manglename none for dmsetup
tests: use get_devs

Check how get_devs is usable with shell array DEVICES
tests: typo
configure: do not exit with error code

Since the test is the last command make a test in a form it will be
after its finished 0.
(regression from last configure cleanup)
tests: adapt test for newline delimit

content of DEVICES is now delimited by newlines
tests: fix test compare

Comparing 64T can't use -eq
tests: disable python failing test

Aborts and needs fixes...
vgchange: Prompt when setting VG cluster attr if cluster is not setup

If clvmd is not running or the locking type is not clustered and someone
attempts to set the cluster attribute on a volume group, prompt them to
see if they are sure.  (Only prompt for one though.  If neither are true,
simply ask them once.)
WHATS_NEW:  For commit 9399b743 (prompt for VG cluster attr change)

Minor change, but put a comment in WHATS_NEW anyway.
vgchange:  With '--yes', don't prompt the user

If the user supplies a '--yes' argument, then don't bother them with
a question to confirm whether to change the cluster attribute (even
if clvmd isn't running).
cleanup: commit c0f9c79 to work also with for non-clustered configuration
cleanup: default.profile is not used (and it was split in two and renamed anyway)
configure: update libcpg test

PKG_CHECK_MODULES needs old-way if;then;fi.