better error messages from libutil

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on July 25, 2014 11:01:07_

We should try to provide more diagnostic information in our error messages from libutil:

"ERROR: failed to register DynamoRIO configuration"

"ERROR: error nudging 8116" (xref Apr 17 email)

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1486_

Start by locating libutil and the code paths that emit the two reported messages: “failed to register DynamoRIO configuration” and “error nudging 8116.” Determine what diagnostic context is available at each failure and inspect existing tests or error-message conventions nearby. Done means both errors provide actionable diagnostic information rather than only their current generic text.

Written by the indexing model from the issue text.