add debug statements to lifo
reset unused lifo slots
macro consistency and more DEBUG

addresses https://github.com/RIOT-OS/RIOT/pull/433#discussion_r8437084
add missing debug statement
make reset of freed slots optional

addresses https://github.com/RIOT-OS/RIOT/pull/433#discussion_r8472602
documentation, remove LIFO_DEBUG, break main

add documentation to lifo.h
remove LIFO_DEBUG and use DEVELHELP instead
make the main method which is included break
fix typo, improve doc
refine DEVELHELP section

more efficient to be better suited for ISR
made testcase more clear
Merge pull request #433 from LudwigOrtmann/lifo_debug

lifo debug and reset
check for __BIG_ENDIAN__ rather than for __BYTE_ORDER__ and include board.h
fix include of crypto
fix native hwtimer

The hardware timer used relative offsets that were never updated
before. This leads to two problems:
a) later timers will get pushed into the future by the amount of
   previous timers
b) if a short timer is set continuously, a longer timer will never be
   called

Example:
a)
Timer a with 500 ms is set, timer b with 600 ms is set.
timer a expires after 500 ms, timer b will be set to expire in 600 ms
which totals to 1100 ms.
b)
Timer a is set to 500 ms, timer b is set to 600 ms.
Timer a expires and is set again. Now timer a will expire in 500 ms
and timer b will be pushed further into the future. Repeating this
will lead to b never expiring.
Merge pull request #463 from LudwigOrtmann/native_hwtimer_fixup

fix native hwtimer
Merge pull request #464 from mehlis/cypto-fix

fix include of crypto
Merge pull request #462 from OlegHahm/endianness

check for __BIG_ENDIAN__ rather than for __BYTE_ORDER__ and include board.h
improve nativenet send functions return type
fix nativenet shell comamnd printf
Merge pull request #465 from LudwigOrtmann/nativenet_send_return

Nativenet send return