core/hwtimer: disable interrupts in hwtimer_remove

Before only the hardware timer's own interrupt was being disabled.
This led to a race condition in the following scenario:

```
Thread1:
    hwtimer_remove()
    hwtimer_arch_disable_interrupt();

// INTERRUPT -> Thread2 (which has a higher priority than Thread1) gets scheduled

Thread2:
    ...
    hwtimer_remove()
    hwtimer_arch_disable_interrupt(); // hwtimer interrupt is already disabled
    ...
    hwtimer_arch_enable_interrupt();
    ...
   // yield | terminate -> Thread1 gets scheduled again

Thread1:
    ... // these instructions are being run with the hwtimer interrupt enabled
    hwtimer_arch_enable_interrupt(); // hwtimer interrupt is already enabled
```

Fixes #924
documentation: fix doxygen for `pthread_*.h`

The pthread header files aren't in the doxygen page anymore after #1137,
because I `@file`'d the `.c` files, not the `.h` files.

This change moves doxygen boilerplate.

Closes #1199.
msp430: workaround: define errno values if not provided by MSP430 lib
native: set _native_pid correctly in daemon mode

This fixes a bug that leads to all unix sockets being created as
`/tmp/riot.tty.0`.
Merge pull request #1213 from OlegHahm/ubuntu_msp430_errno_fix

msp430: workaround: define errno values if not provided by MSP430 lib
Merge pull request #1216 from LudwigOrtmann/issue-1215

native: set _native_pid correctly in daemon mode
Merge pull request #1208 from Kijewski/issue-1199

documentation: fix doxygen for `pthread_*.h`
core: kernel: improved doxygen documentation

also added param[in] to irq.h and fix order of doxygen endguards
Merge pull request #977 from mehlis/doxygen-irq

core: kernel: improved doxygen documentation
Merge pull request #1193 from LudwigOrtmann/issue-924

core/hwtimer: disable interrupts in hwtimer_remove
examples: added README.md to ccn-lite-client and relay