Fix FTBFS in many arches due to FS tests

The cause is that it cannot find /etc/mtab (or equivalent) in some arches.  The
new standard place for this is '/proc/self/mounts'.  "./configure
 --with-mnttab='/proc/self/mounts'" does not seem to work.
fix configure gives --with-mnttab a higher prio
fix missing "x" typo
Add support for FreeBSD 11+.

This change adds support for FreeBSD 11, and onwards up to 19. I've
also changed the comment to correct reflect that it's FreeBSD 5+,
rather than specifically 5 to 11.

Mostly solves #26.
Make sure the test target builds dependencies.

The test target can only be run after the tests and the libstatgrab
library have been built, otherwise it reports that there's nothing
to test:

Result: NOTESTS

This change only builds the required dependencies, so it won't build
the examples or manpages.
Break the ChangeLog generation up.

This used to be split over multiple lines when it was in the Makefile,
but I concatenated it by mistake when bringing it across to here.
Add missing brackets in AC_INIT.

This was suggested by autoupdate.
Fix PIPD_IS_FULL.

PIPD_IS_FULL wasn't correctly identifying pipd being full which
resulted in the add_pid_to_pids_in_proc_dir function walking off
the end of the allocated memory structure. This caused the breakage
seen in #38.

The problem was found using the Solaris watchmalloc library.
Fix compiler warning created in commit dd23b3b.

  process_stats.c:189:6: warning: comparison of integers of different signs: 'unsigned long' and 'ssize_t' (aka 'long') [-Wsign-compare]
          if( PIPD_IS_FULL( pipd, sys_page_size ) ) {
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  process_stats.c:182:95: note: expanded from macro 'PIPD_IS_FULL'
  #define PIPD_IS_FULL(pipd,size) (offsetof(struct pids_in_proc_dir_t, items[(pipd)->nitems+1]) > (size))
                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
resolve symbolic links on device names

If a device name is a link, resolve the link and compute canonical path
name from it. Some modern systems use device-independent identifiers
with a symlink to the physical device to avoid different order of registering
during boot causes trouble.
eliminate some -Wunused-result warnings
add strlcat/strlcpy checks

Without them tools.h will always pretend sg_strlcat should be strlcat
which causes redefinition warnings. Remove libstatgrab-wide export of
internal strlcat - helpers sg_log_init is integrated and the routines
are internal only now.
fix compiler warning

This fix is to eliminate:

    full_stats.c:134:10: warning: passing argument 1 of 'get_testable_functions' from incompatible pointer type
    full_stats.c:134:68: warning: incompatible pointer types passing 'unsigned long *' to parameter of type 'size_t *' (aka 'unsigned int *') [-Wincompatible-pointer-types]
fix unused variable for logging ...

    process_stats.c:772:11: warning: unused variable 'failing_pid'
    process_stats.c:1070:10: warning: variable 'p' set but not used [-Wunused-but-set-variable]