boards/mbed_lpc1768: disable DEBUG by default

Set ENABLE_DEBUG from (1) to (0)
cpu/sam3x8e: fixes to timer driver

- renamed config variable
- placed thread_yield() correctly
cpu/sam3x8e: put PendSV IRQ to lowest prio
cpu/sam3x8e: added output to isr_hard_fault
cpu/sam3x8e: fixed style in startup.c
Merge pull request #1825 from haukepetersen/fix_sam3x_misc

cpu/sam3x8e: general fixes
core: eliminate warning

This initialized has actually no relevance and is just needed to
suppress a compiler warning.
core: update irq_arch documentation
Merge pull request #1901 from OlegHahm/hwtimer_irq_fixup

core: eliminate warning in hwtimer
core: move optional tcb members to DEVELHELP
native: remove obsolete line
sys: Initial import of analytical object dump (od) module
Merge pull request #1884 from authmillenon/od

sys: Initial import of analytical object dump (od) module
Merge pull request #1815 from OlegHahm/core_eliminate_unnecessary_tcb_members

core: eliminate unnecessary tcb_t struct fields
Merge pull request #1899 from Lotterleben/rm_debug_mbed_lpc1768_hwtimer

boards/mbed_lpc1768: disable DEBUG by default