logging: Add LCK_REVERT_MODE to flags printed by decode_flags()

The decode_flags() function does not yet know about the
LCK_REVERT_MODE flag.
cleanup: fix compiler warning

locking/file_locking.c:162:2: warning: implicit declaration of function ‘init_signals’
make: fix commit 1756bf6

"DIST_TARGET" should be "DISTCLEAN_TARGET"
locking: use sigaction signal handling

Use sigint_allow/restore function instead of duplicating code
and switch to use only sigactiction based signal handling.
debug: add more debug message for signal handling

Adding log_sys_debug for eventual logging of system errors.
(Using debug level, since currently signal handling functions
do not fail when any error is encoutered).
signals: better nesting support

Support upto 3 levels os nesting signal blocking.
As of today - code blocks signals immediatelly when it opens
VG in read-write mode - this however makes current prompt usage
then partially unusable since user may not 'break' command
during prompt (something most user would expect).

Until a better fix for prompting is implemented, put in support
for signal nesting - thus when prompt enables signal acceptance,
make it possible to really break command at this point.
cache: avoid expression overflow

Cast data_extents to 64bit so calculation is in 64b arithmetic.
coverity: check for profile

Ensure str is not NULL for analyzer.
coverity: error for undefined origin

If we would have been missing origin here, it would
be an internal error - since these values are validated
earlier.
coverity: ignore ret val

Since we intentionaly do not want to check them,
cast result values to void.
cleanup: drop uneeded headers
cleanup: cosmetics.

Initialized attrs so analyzers are less confused
(since currently our method calls should always initialize attrs on
return).
cleanup: missed conversion to dm_malloc/free usage

Few missed unconverted dm_malloc/free calls.
clenaup: drop unused assigns
cleanup: constify pointers
cleanup: use enum return codes
configure: drop siginterrupt

Not used anymore
configure: improve needs_check thin_check test

Improve testing for needs_check - when old tools are installed,
issue proper warning from configure, but stop sending needs_check
flag to the old tool.
coverity: catch unwanted path

We validate this path already earlier.
conf: document new thin_check option