make: initialize debugger with TERMFLAGS
added missing `extern "C"` guards
 core: make sched_runqueues static

 PR #1000 overlooked to rename `runqueues` into `sched_runqueues` in
 `sched.h`. This shows that the variable is not used outside of
 `sched.c`.

 As the list should not be accessed outside of the scheduler, so it
 can be `static`.
Merge pull request #1816 from Kijewski/runqueues-name-fixup

 core: make sched_runqueues static
make: doc: clean up dist Makefile
Merge pull request #1858 from OlegHahm/dist_makefile

make: doc: clean up dist Makefile
Merge pull request #1851 from authmillenon/native-debug-args

make: initialize debugger with TERMFLAGS
Merge pull request #1856 from BytesGalore/extern_C_in_headers_drivers_add_new_headers

drivers: added missing `extern "C"` guards in new files
cpu/cc2538: added linkerscript for cc2538sf53
boards: added support for OpenMote
cpu/cc2538: cleaned up IRQ vector definition
cpu/cc2538: centralized all cpu specific includes

- added all CPU specific includes to cpu-conf.h
- removed now not needed includes from cpu .c files
cpu/cc2538: adjusted GPIO register definitions