Fix for subject lines with invalid UTF-8 as the last character

This seems to be the bug mentioned here:

  http://po-ru.com/diary/fixing-invalid-utf-8-in-ruby-revisited/

That explains that some versions of Iconv don't ignore
invalid characters when converting to UTF-8 even with
//IGNORE if that invalid character happens to be at the end
of the string.  In fact, as Matthew Somerville pointed out,
with some versions of iconv (e.g. 1.14 on Mac OS, apparently)
it's necessary to add and remove more than one space at the end,
in case the first character of the byte sequence indicates a
long sequence.  We add and remove 4 to be on the safe side.
Parse the 'to' address as if on a real mail to trigger quoted string encoding.
 Replace backticks with call to exec(), the former spawns a new process, and the latter replaces the current process. In the daemon context we care about the process id so that calls to startstopdaemon won't spawn a new daemon.
For non-HTML requests, just return the response code for now.
Handle json requests for hidden info requests.
Restore public body edit form.
Merge branch 'hotfix/0.11.0.1' into release/0.11