This fixes the following AC warning:
```
configure.ac:6: warning: AM_INIT_AUTOMAKE: two- and three-arguments forms are deprecated. For more info, see:
configure.ac:6: https://www.gnu.org/software/automake/manual/automake.html#Modernize-AM_005fINIT_005fAUTOMAKE-invocation
```
As per the deprecation notice, using `AM_INIT_AUTOMAKE` for setting the
version is mostly obsolete because the package and version can be obtained
from Autoconf’s `AC_INIT` macro.
When there's no pkg-config file for the panel library, the build breaks
if the header is not in /usr/include.
At least in openSUSE, we have /usr/include/ncurses.h and
/usr/include/ncurses/panel.h.
