Add explicit support for being installed into a system triggered with --enable-fhs...

Add explicit support for being installed into a system triggered with --enable-fhs-paths.
Add two mechanism for avoiding name-collisions in a system-wide installation of charybdis. The ssld and bandb daemons, intended to be directly used by ircd and not the user, install into libexec when --enable-fhs-paths is set. For binaries which are meant to be in PATH (bindir), such as ircd and viconf, there is now an option --with-program-prefix=progprefix inspired by automake. If the user specifies --with-program-prefix=charybdis, the ircd binary is named charybdisircd when installed. Add support for saving the pidfile to a rundir and storing the ban database in localstatedir instead of in sysconfdir. This is, again, conditional on --enable-fhs-paths. Fix(?) genssl.sh to always write created SSL key/certificate/dh parameters to the sysconfdir specified during ./configure. The previous behavior was to assume that the user ran genssl.sh after ensuring that his current working directory was either sysconfdir or a sibling directory of sysconfdir.