Log Message:
Update to 0.21:

 - Clean up perl_src path using Cwd::realpath().  Only affects usage
   as part of the perl core.

 - Protect $., $@, $!, $^E, and $? from any clobbering that might
   occur in our DESTROY method. [Zefram]

 - From bleadperl, a patch to clean up debug symbol files (.pdb for
   VC++, .tds for BCC) when running have_compiler(). [Steve Hay &
   Steve Peters]