test_errpfx was setting two data dirs.  exceptions is broken out to its worn rule (and is failing because of #2284).  exceptions was also operating in the cwd, instead of a subdir.  The reverse_compare_fun was failing because it wasing cwd for some calls instead of the subdir. Refs #2285, #2284.  [t:2285] [t:2284]

git-svn-id: file:///svn/toku/tokudb@16835 c7de825b-a66e-492c-adef-691d508d4ae1