DB->open, and DB->remove now use the data dirs
We look (in order) in each of the data dirs for a file to open/remove.
The first file found, is the one used (even if another is similarly named with
different subdbs).

For creating dbs, (if file does not exist in any of the search dirs), we always
create in the first data dir (or env->i->dir if no data dirs are set).

Addresses #42
Addresses #108


git-svn-id: file:///svn/tokudb@1304 c7de825b-a66e-492c-adef-691d508d4ae1