shell: refactor default shell command handling

before, we actually duplicated code for handling of shell commands
supplied to shell_init and those hardcoded by MODULE_SHELL_COMMANDS.

This patch refactors shell.c find_handler and print_help so there's
no duplicated code.
make TCP in destiny optional
hwtimer.h remove cruft, document, rearrange

remove unsused hwtimer_t0* declarations
document hwtimer_now
move hwtimer_now outside the internal section
initializes watchdog properly for MSB-A2

It the watchdog does not reset the WDMOD, BSL pin remains ignored.
include version string
only add branch to version string if not in master
get rid of static buffer

this buffer was used for two types of outgoing packets:
  1. local msg
    - msg can be big, there is is no apriori boundary -> use dynamic
      memory instead
  2. transceiver msg
    - no need to copy msg in this buffer -> transceiver send is blocking
tune CCNL_RIOT_CHUNK_SIZE

this constant is used for two test cases:

1. populate + interest /riot/text
  -> static content has this=90 bytes size

2. appserver + interest /riot/appserver/test
  -> dynamic content is created with exact
     CCNL_RIOT_CHUNK_SIZE bytes
  -> CCNL_RIOT_CHUNK_SIZE can be any value the
     transceiver can handle
make max_cache_entries a parameter
fix: remove oldest dynamic entry in content store
enable timeout events
fix function declaration isn't a prototype
fix native stdlib.h include

Fixes segfault in OSX introduced by 45ffdea
shell: fix compile warning and add some comments
Merge pull request #389 from mehlis/ccn-lite-follow-up-2

Ccn lite follow up
Merge pull request #337 from LudwigOrtmann/hwtimer_cleanup

hwtimer.h remove cruft, document, rearrange
Merge pull request #351 from OlegHahm/tcp_optional

make TCP in destiny optional
Merge pull request #394 from LudwigOrtmann/native_fix_include

fix native stdlib.h include
Merge pull request #378 from OlegHahm/version_string

include version string
Merge pull request #380 from OlegHahm/fix_watchdog

initializes watchdog properly for MSB-A2