On a failure to cache a symbol lib, don't skip subsequent libs

By rethrowing the exception here, the entire caching process is
curtailed if there is an IO_ERROR while parsing a lib. This means any
libs up to the one before the bad one will be cached, but ones after it
wil not be.

Change to wxLogError to gather the errors to present to the user at the
end of the process.

eeschema/class_library.cpp

@@ -1059,7 +1059,7 @@ void PART_LIBS::LoadAllLibraries( PROJECT* aProject ) throw( IO_ERROR, boost::ba
                     GetChars( ioe.What() )
                     );
 
-            THROW_IO_ERROR( msg );
+            wxLogError( msg );
         }
     }