shell: print command if not found
shell: fixup test_shell expect scripts
shell: fix newlines
x86: add read-before-write check at runtime

Finding read-before-writes statically is quite difficult. In native we
can use valgrind, but on boards without an MMU we are out of luck.

x86 has an MMU, let's use it.

If `-DDEBUG_READ_BEFORE_WRITE` was set, then pages on the heap get
initialized upon first use. If the page was read before written, then a
debug message with the virtual and physical address of the memory
location is printed, as well as the address of the offending instruction.
drivers: added rgbled driver
Refactored crypto module into structured directoy layout

* crypto ciphers now located in sys/crypto/chipers/*
* crypto hashes now located in sys/crypto/hashes/*
Added block cipher mode operation support

The following cipher modes are now supported
* Electronic code book (ECB)
* Cipher block chaining (CBC)
* Counter (CTR)
* Counter with CBC-MAC (CCM)
Fix undefined references issues for pow

Linker (for gcc < 4.9) is complaining about missing math functions
(like pow) even though we have -lm in "Makefile.include". If we put
"-lm" as last statement it just works.
Added unittests for crypto aes operations
Renamed ciphers from MODULE_CIPHERS_<name> to MODULE_<ciphername>