qibuild.dlls: subtle bug fix
qibuild.dlls: subtle bug fix

dest was not always created, so
qibuild.sh.install(dll, dest) copied the dll in a *file* named 'bin',
causing lots of 'intersting bugs'

Change-Id: Idb111024193e27633ecdd62bbe887a847debde77
Reviewed-on: http://gerrit.aldebaran.lan:8080/422
Reviewed-by: dmerejkowsky <1e4b13000fa8777df4cefd2fd8215187e3deb062@aldebaran-robotics.com>
Tested-by: dmerejkowsky <1e4b13000fa8777df4cefd2fd8215187e3deb062@aldebaran-robotics.com>

dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild