Make P4Ruby's build script support the const_char macro definition
on those platforms that need it (Solaris >= 2.7 and Linux on AMD64
primarily). If we ever port P4Ruby to LinuxIA64 we'll need to
add support for that too.
With this change p4conf.rb tries harder to determine the O/S name
and version, but it's unlikely to get it right all the time. So
there's also a new '--apibuild' flag to p4conf.rb that allows
the user to override the detected platform with an explicit
configuration. Most people won't have to use it, but it'll be
there for those that need it.
I've also updated the README with the new build procedure, and
added a FAQ document for the most common questions.