Enabled the namespace-specific search functionality,

which had previously been commented out while I tested
it.  It's not fully working yet, but it doesn't break
our testsuite and it's an important piece of
functionality.

Also added some logging to SymbolFileDWARF to help
diagnose entities that are found in a symbol file,
but do not reside in the expected namespace.

llvm-svn: 141894