cascalog.io/with-fs-tmp's root dir now is configurable

I'm getting back to https://groups.google.com/d/topic/cascalog-user/523iptcITWM/discussion.

Please consider this pull request an attempt. Certainly there are things to be discussed here:

- the general approach (to use jobconf to configure the root directory for "cascalog_reserved")
- the name of the configuration variable: "cascalog.tmpdir"
- whether it is reasonable to consider "cascalog_reserved" a reserved place where Cascalog dwells and just provide a way to configure under which directory it is hooked

Looking forward to getting feedbak on this!


From (doc 'cascalog.io/with-ts-tmp'):

with-fs-tmp generates unique, temporary path names as subfolders of
<root>/cascalog_reserved. <root> by default will be '/tmp', but you
can configure it via the JobConf property 'cascalog.tmpdir'.