examples/rpl_udp: use defaulttransceiver
Make: exterminate 'clean' buildtarget

Closes #993.

We do not need to descend into the modules to know what to do on
`make clean BOARD=blub`. We can just invoke `rm -rf bin/blub`.

This PR only keeps the descending into the USEPKGs, since they might
want to delete cached/downloaded/extracted data.
vtimer: fix integer overflow in vtimer_now() for MSP-430
Add missing doxygen for pthread funs and structs
pthread: fix spinlock
ccnl: use default transceiver
Merge pull request #1021 from Kijewski/vtimer_now-no-16bit-overflow

vtimer: fix integer overflow in vtimer_now() for MSP-430
core: fix warning about discarding volatile
Merge pull request #1027 from mehlis/core-tcb-warning

core: fix warning about discarding volatile
Merge pull request #969 from LudwigOrtmann/examples_rpl_udp_defaulttransceiver

examples/rpl_udp: use defaulttransceiver
Merge pull request #1001 from mehlis/ccnl-defaulttransceiver

ccnl: use default transceiver
Merge pull request #1017 from Kijewski/issue-980

documentation: Add missing documentation for pthread functions and structures
Merge pull request #995 from Kijewski/issue-993

Make: exterminate 'clean' buildtarget clutter
pthread: implement reader/writer lock
Add pthread_rwlock test
Merge pull request #1018 from Kijewski/pthread-rwlock

pthread: implement reader/writer lock