Steps to reproduce the issue

Make a file only readable (r--r--r--) that should be replaced by component update .
Start update

Expected result

-1 An error occured
Copy failed to

Actual result

-1 An error occured
Copy failed

System information (as much as possible)

J3.3.6
PHP 5.4 , 5.5
Linux 12.04 , 14.04
Akeeba backup 1.5.5 (component to be updated)

Additional comments

Current message leaves user in the dark and has no clue where to start looking for the problem

Proposed fix

File : /libraries/joomla/filesystem/file.php
if (!@ copy($src, $dest))
{ JLog::add(JText::sprintf('JLIB_FILESYSTEM_ERROR_COPY_FAILED',$src,$dest), JLog::WARNING, 'jerror');

return false;
}

File: /language/en-GB/en-GB.lib_joomla.ini
JLIB_FILESYSTEM_ERROR_COPY_FAILED="Copy failed %s to %s"