Stopped to load plugins depending on simulations if there is no simulation
collect: making some protocol parameters configurable by COLLECT_CONF_ style defines

TTL (which has a rather low default of 15), MAC level retransmissions,
overall number of retransmissions, and the header bits dedicated to these
were all fixed in the collect.h and collect.c, without a simple way to
override them.
Extracted these as COLLECT_CONF_ parameters, keeping defaults as they were
before.

Signed-off-by: Csaba Kiraly <kiraly@disi.unitn.it>
rl78: Rename CORE to RL78_CORE to avoid a conflict with Contiki's CORE variable.
eval-adf7xxxmb4z: Corrections to the platform README, update URLs to point to the mainline Contiki.
rl78: Attempt to locate the IAR installation automatically and instruct the user how to specify IAR_PATH if it cannot be found.
Merge pull request #538 from cskiraly/collect-fixes

collect: making some protocol parameters configurable by COLLECT_CONF_
eval-adf7xxxmb4z: Use the nullrdc driver instead of sicslowmac.
Adds  encoding attribute utf-8 arg to cooja compile command
Merge pull request #544 from drakkar-lig/cooja-compile-error

Cooja compile error
Merge pull request #532 from darki2002/Plugin_sim

Stopped to load plugins depending on simulations if there is no simulation
Merge pull request #540 from hexluthor/rl78-fixes2

More fixes for the RL78 / EVAL-ADF7xxxMB4Z platform
cc2538: Fix library linkage

If a project needs to use some libraries at link stage, then the corresponding
linker options (e.g. '-lm') have to be passed after any .o file depending on
these libraries. Hence, LDFLAGS cannot be used to add such options when invoking
$(LD) in Makefile.cc2538, or it should be moved to the correct location.
Instead, this change adds TARGET_LIBFILES to the correct location, like most
other Contiki targets.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Merge pull request #545 from ADVANSEE/cc2538-lib-link

cc2538: Fix library linkage