vtimer: fix callback usage

There is no need to test the "handler" set in the vtimer struct, and
have some code executed then. We just can make the code to execute the
handler. To lengthy `if else if`, just a call.
lpc1768: cleanup Makefile

`cpu/lpc1768/Makefile` contains many lines that don't belong into this
file, but the maybe `Makefile.include`. Either way, this Makefile is
never called with these goals.
Fix all warnings for native and qemu-i386

Missing returns, unused variables (only used for debugging), empty
translation units, missing function prototypes, and GNU extensions.
native: implement hwtimer removal
nativenet: change max packet size to 127

Real IEEE 802.15.4 transceivers have a payload of 127. Hence, for
testing - particular 6lowpan - it would make sense to have the same
limitation in nativenet. Especially to test fragmentation this is
helpful.
cpu cortex-m3_common: cleanup thread_arch.c
cpu - sam3x8e: added switch for newlib-nano specs
Merge pull request #1354 from OlegHahm/nativenet_packetsize

nativenet: change max packet size to 127
Merge pull request #1335 from Kijewski/fix-all-warnings-for-native-and-qemu-i386

Fix all warnings for native and qemu-i386
cpu - sam3x8e: fixed vtimer, added timer_set_absolute
Merge pull request #1356 from haukepetersen/fix_sam3x_newlibnano

cpu - sam3x8e: added switch for newlib-nano specs
Merge pull request #1357 from haukepetersen/fix_cortexm3_threading

cpu: cortex-m3_common: cleanup thread_arch.c
Introducing a source routing header for RPL.
Merge pull request #1218 from fabianbrandt/srh_rpl

Introducing a source routing header for RPL.
boards: removed -lto flag and cleanup for udoo&arduino due
Merge pull request #1365 from haukepetersen/fix_cortexm3_ltoflag

boards: removed -lto flag and cleanup for udoo&arduino due
Merge pull request #1358 from haukepetersen/fix_sam3x_vtimer

cpu - sam3x8e: fixed vtimer, added timer_set_absolute
Merge pull request #1187 from Kijewski/mbed_lpc1768-makefile-cleanup

lpc1768: cleanup Makefile
Split RPL into core and mode related functions.
drivers - gpio: expanded gpio driver interface

- added functions for en|disabling a pins interrupt