Makefile.am: moving check_ctags to a target
Makefile.am: moving check_ctags to a target

Calling a shellscript within a Makefile is not POSIX compliant, it's
possible that it would not work on all platforms. But using the check
for ctags as a seperate target within the main Makefile is no problem
and easy to change.

This commit is a addition to 101efbfe6940fd471530fb2511def7f3862ad0d0

authmillenon/libcoap,gebart/libcoap,authmillenon/libcoap,authmillenon/libcoap,gebart/libcoap,gebart/libcoap