Let's take an example:

fd = open(..) /* fd = 3 for example */

lxc_mainloop_add_handler(descr, fd, cb1, data1) fails.

the program take care of the error, it closes the fd

Later, reopen a fd (get 3 for again)

lxc_mainloop_add_handler(desc, fd, cb2, data2) is ok.

When something happen on fd, cb1 with data1 will be called instead of
cb2 with data2, because descr->ev contains 2 entries for fd == 3.
Signed-off-by: Clement Calmels <clement.calmels@fr.ibm.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>