Makefiles: Allow setting UIP_CONF_IPV6=0 to work as expected.

Setting UIP_CONF_IPV6 to zero from the make build command line is
something that seems like it should ensure that IPv6 is disabled, but in
fact it actually *enables* IPv6. This seems counter intuitive, so this
patch changes the behavior of the makefiles to handle this case
properly.
Added missing include of contiki-conf.h
Load Makefile.target for slip-radio

This loads Makefile.target into Makefile so we can check for TARGET==sky
when building this. Compilation for sky fails without it.

Signed-off-by: Johannes Gilger <heipei@hackvalue.de>
platform/minimal-net: Implement better idle behavior.

The minimal-net target, as currently written, wakes up the
CPU every millisecond to check for packets, and will only
react in real-time to input from stdin. If you are running
this on a laptop battery, your battery will quickly drain.

This change allows the CPU to idle when there is literally
nothing to do while still being responsive to input from
stein and/or incoming packets. This fix should significantly
improve performance while significantly improving power
usage. Win-win.

Also added `_xassert()` implementation so that the contiki-
provided `assert()` macro will work properly when used
on this platform.
platform/minimal-net: Better, more seamless support for OS X.

This patch enables automatic route setup and cleanup when
starting and stopping the minimal-net target on OS X.

Both IPv4 and IPv6 are supported.

Using the minimal-net target on OS X was absolute hell
before I came up with this patch. Now it is painless.
platform/minimal-net: Print out pseudo LED status.
Makes RPL Initial Link Metric configurable
Bug fix: changed the macro RPL_LOLLIPOP_INCREMENT to update the counter instead of returning the new value since this is how the macro is used today.
add_timer() does not set owning process
one blank less
Add some debug PRINTFs for RPL_LEAF_ONLY mode.
Update cpu/native/Makefile.native
httpd-simple-avr: 'isused' seems to not be used anymore.
Merge pull request #142 from malvira/rpl-leaf-debug

Add some debug PRINTFs for RPL_LEAF_ONLY mode.
Merge pull request #126 from rgrr/master

Bug fix: add_timer() does not set owning process
Merge pull request #125 from nfi/lollipop

Bug fix: corrected the macro RPL_LOLLIPOP_INCREMENT
Merge pull request #102 from cetic/rpl-conf-init-link-metric

Makes RPL Initial Link Metric configurable
Merge pull request #99 from heipei/slip-radio

Load Makefile.target for slip-radio
Merge pull request #90 from simonduq/rpl-conf

Added missing include of contiki-conf.h in rpl-conf.h
Merge pull request #137 from darconeous/pull-requests/platform-avr-ravenusb-httpd-isused-fix

Fix for avr-ravenusb target builds due to missing 'isused'.