!bug: a bad typo (FUNC_NAME -> FUNCNAME)

$FUNCNAME is a Bash variable, that presents the current function
name. In our case, it is "_OSTYPE_detect". (I hope that the binary
"pacman" will not have this string.)

Ok, bug yields another bug. By using FUNC_NAME, the :grep will
always return true, and there is still a loop.

Thanks to :Severus and :kitarousa for your time ;)

FIXME: use Bash -e
FIXME: provide tests for :pacapt