Less obscure error messages

[pjlegato]

Currently, exceptions are generated like:

 java.lang.IllegalArgumentException: Don't know how to create ISeq from: net.cgrand.enlive_html$html_content$fn__17289

It's unclear what caused this, particularly as the line number given in the corresponding stack trace is usually incorrect due to macro rewrites. An (at) form might have many elements being updated; there is no way to tell which one caused the error

Could the error message in the exception be updated somehow to include the name of the offending element and/or the erroneous data that the user attempted to insert there?