Cleaned up various fragments and fixed a compilation error that occured when switching metric container.

Fixed a wrapping problem in the ETX EWMA calculation.

Corrected the multiplier of the link metric, and simplified the configuration
so that the user does not need to specify the multiplier.
Set peripheral mode for the correct UART TX/RX pins
Merge pull request #361 from nvt/rpl-mrhof-fix

MRHOF fixes
Fixed printout that used deprectated rpl_parent_t structure
Reverted commit below as the cc65 bug in question is fixed.

Rearranged some expressions to avoid triggering a cc65 bug. (reverse-merged from commit 7134da0915cf56c7eeff2cd22b6b3ddeff5e7e33)
Merge pull request #381 from oliverschmidt/master

Reverted commit below as the cc65 bug in question is fixed.
Merge pull request #380 from simonduq/fix-rpl-of0

Fixed printout that used deprectated rpl_parent_t structure
[core/net/mac] Removed invalid struct member u8 in PRINTADDR
Merge pull request #382 from ejoerns/pull-req/core/net

core/net/mac: Invalid struct member u8 in PRINTADDR
Merge pull request #365 from g-oikonomou/cc2538-uart-init-fix

Set peripheral mode for the correct CC2538 UART TX/RX pins
Bumped the version number from Contiki 2.6 to Contiki 2.7
Merge pull request #402 from adamdunkels/release-2-7

Bumped the version number from Contiki 2.6 to Contiki 2.7
Merge remote-tracking branch 'upstream/release-2-7' into develop