configure.ac, Makefile.am, smartd.cpp, smartd_warning.sh.in:
Add '--with-smartdscriptdir' configure option to change location of
smartd_warning.sh (Debian bug 710815).
Add '--with-smartdplugindir' configure option to change (or disable)
smartd_warning.sh plugin location.
smartd.conf.5.in: Optionally hide the plugin documentation.

git-svn-id: https://svn.code.sf.net/p/smartmontools/code/trunk/smartmontools@3932 4ea69e1a-61f1-4043-bf83-b5c94c648137