Bugs with readMenu*().

Bugs with readMenu*().

readMenuPipe() was calling freeline() on stuff which might be uninitialised, causing
a crash if no valid input was read.

readMenuPipe() was trying to snprintf() on an uninitialised pointer.  We now use a
fixed-length buffer like the other readMenu*() functions.

Various memory leaks in readMenu*() functions have been fixed.  There
are still some lurking around but most have been removed.

The original report from Charles Philip Chan <cpchan@bell.net> on 22 May 2012 says
that:

"Window Maker crashes when I try to open a sub-menu auto-generated by using:
 xdg_menu --format WindowMaker --charset UTF-8"

There was also a report from Amadeusz Sławiński <amade@asmblr.net> on 24 May 2012
stating that wmaker crashes using:

% cat test.sh
cat << EOF
Test MENU
stuff EXEC true
Test END
EOF

% grep test GNUstep/Defaults/WMRootMenu
  ("Generated Submenu", OPEN_MENU, "|| /home/amade/test.sh")

Error is:
wmaker(MonitorLoop(monitor.c:134)): warning: Window Maker exited due to a crash (signal 11) and will be restarted.