Rework spec handling somewhat so that:
(a) P4Ruby knows about the default spec types for 2007.2 so it
doesn't have to connect to the server to parse and format specs,
and nor does it have to do the ugly hack of running a 'p4 xxx -o'
and discarding the result just to get the specDef.
(b) If a user's got a custom spec then the spec cache will be updated
if they fetch an object of that type. So basically, if the
server's given us a specdef for a class of spec, we use it.
Otherwise, we fall back on the builtin defaults
This reworks SpecMgr quite a bit - renaming methods so it's clearer
what they do, and making it own the spec cache. We also pass the
SpecMgr object created by P4ClientApi down to ClientUserRuby now,
so that whenever the server sends us a spec, we can update the cache.