Fix value returned by smack_label_length()

In some cases smack_label_length have returned 0 on incorrect label.
Now smack_label_length() always returns -1 in case of incorrect label.
Use smack_label_length() internally instead strnlen()

Use smack_label_length() to check correctness labels instead strnlen().
Fix man pages

Regression from 1edba54.
Regression fix: don't modify smack_accesses while applying the rules.

Regression introduced in eaf908fd caused access_type field to be modified,
when smack_accesses_apply() is called with clear set to true.

This patch reverts that, restoring invariant that smack_accessess_apply()
doesn't modify given rule set.
Fixed copyright clauses.

Checked that copyright notices are properly set up as according to:

http://www.gnu.org/licenses/gpl-howto.html

Corrected where they are not. Note that one or two-line fixes do not
count as copyrightable assets.

Additionally, fixed a minor indentation issue in chsmack.c.
Use strncpy() always copying labels.

Defence in depth and a good practice. Places an absolute limit
to the length copied.
Merge remote-tracking branch 'jarkkos/copyright-fix'
Merge remote-tracking branch 'jarkkos/strcpy-fix'
Helper function get_label()

The helper function ssize_t get_label(char *dest, const char *src)
validates the given label and copies it to the dest buffer if
available.
Copy labels using get_label()

Copy and validate labels in a single transaction:

- No trust for having '\0' in the src buffer when copying
  labels.
- Improves performance by combining length calculation, validation
  and copying.
Generate API documentation by using Doxygen.

Generate API documentation from smack.h by using Doxygen so that
documentation needs to be maintained only in one place.
Solve problem with "make distcheck" breaking on systemd config files.

Dist packages created by "make dist" were built without smack.mount and
smack.service files. This caused the packages to fail to build.
Adding the files to EXTRA_DIST solves the problem.
Merge remote-tracking branch 'jsakkine/issue45'
debian: fix package build, broken by c5e2007.

Auto generated manpages are in different locations than static ones, so
libsmack-dev.manpages needs to be modified.
It now includes all generated section 3 manuals.
doc: fix parallel build, broken by c5e2007.

Parallel make failed, because dependencies were not properly specified
for all auto generated man pages.
doc: show version

Fix documentation to show correct package version.
utils: fix CIPSO error messages in common.c

When applying CIPSO fails use different error message than when
applying access rules. Additionally, fixed indentation for lines
printing error message that are over 80 characters long.