examples/bot: removed non-standard strcpy_s/strcat_s

strncpy/strncat must be used instead. But in this case they don't make
sense, because string has enough space.
autotools: removed libresov check for freebsd.
autotools: cleaned up configure.ac and Makefile.am
autotools: check for expat.h if pkg-config failed

Some distros provides libexpat without expat.pc. So PKG_CHECK_MODULES
fails even if libexpat is installed. To fix this AC_CHECK_HEADER added
back.
Merge branch 'master' of https://github.com/strophe/libstrophe

Conflicts:
	configure.ac