make: add comprehensive `buildinfo` list

Sometimes it is difficult to track down build errors for boards that you
are unfamiliar with.

This change adds `make buildinfo` that prints out all the relevant build
information for the selected board and project:

```
PROJECT: default
BOARD:   msba2
CPU:     lpc2387
MCU:     lpc2387

RIOTBASE:  /home/kijewski/RIOT/RIOT
RIOTBOARD: /home/kijewski/RIOT/RIOT/boards
RIOTCPU:   /home/kijewski/RIOT/RIOT/cpu

DEFAULT_MODULE: auto_init core cpu sys
DISABLE_MODULE:
USEMODULE:      arm_common cc110x_ng cc110x_spi config defaulttransceiver gpioint lib lpc_common ltc4150 mci net_help posix protocol_multiplex ps random rtc shell shell_commands sht11 timex transceiver uart0 vtimer

ELFFILE: /home/kijewski/RIOT/RIOT/examples/default/bin/msba2/default.elf
HEXFILE: /home/kijewski/RIOT/RIOT/examples/default/bin/msba2/default.hex

CC: arm-none-eabi-gcc
CFLAGSS:
        -DBOARD_MSBA2
        -DCPU_LPC2387
        -DMODULE_ARM_COMMON
        -DMODULE_AUTO_INIT
        -DMODULE_CC110X_NG
        -DMODULE_CC110X_SPI
        -DMODULE_CONFIG
        -DMODULE_CORE
        -DMODULE_CPU
        -DMODULE_DEFAULTTRANSCEIVER
        -DMODULE_GPIOINT
        -DMODULE_LIB
        -DMODULE_LPC_COMMON
        -DMODULE_LTC4150
        -DMODULE_MCI
        -DMODULE_NET_HELP
        -DMODULE_POSIX
        -DMODULE_PROTOCOL_MULTIPLEX
        -DMODULE_PS
        -DMODULE_RANDOM
        -DMODULE_RTC
        -DMODULE_SHELL
        -DMODULE_SHELL_COMMANDS
        -DMODULE_SHT11
        -DMODULE_SYS
        -DMODULE_TIMEX
        -DMODULE_TRANSCEIVER
        -DMODULE_UART0
        -DMODULE_VTIMER
        -O2
        -Wall
        -Wstrict-prototypes
        -mcpu=arm7tdmi-s
        -gdwarf-2
        -std=gnu99
        -fno-delete-null-pointer-checks
        -Wstrict-prototypes
        -Werror=strict-prototypes
        -Wold-style-definition
        -Werror=old-style-definition

LINK: arm-none-eabi-gcc
LINKFLAGS:
        -gdwarf-2
        -mcpu=arm7tdmi-s
        -static
        -lgcc
        -nostartfiles
        -T/home/kijewski/RIOT/RIOT/cpu/lpc2387/linkerscript.x

OBJCOPY: arm-none-eabi-objcopy
OFLAGS:  -O ihex

FLASHER: lpc2k_pgm
FFLAGS:  /dev/ttyUSB0 /home/kijewski/RIOT/RIOT/examples/default/bin/msba2/default.hex

TERMPROG: /home/kijewski/RIOT/RIOT/dist/tools/pyterm/pyterm.py
PORT:     /dev/ttyUSB0

DEBUGGER:
DEBUGGER_FLAGS:

MAKEFILE_LIST:
        /home/kijewski/RIOT/RIOT/examples/default/Makefile
        /home/kijewski/RIOT/RIOT/Makefile.include
        /home/kijewski/RIOT/RIOT/Makefile.modules
        /home/kijewski/RIOT/RIOT/Makefile.pseudomodules
        /home/kijewski/RIOT/RIOT/Makefile.defaultmodules
        /home/kijewski/RIOT/RIOT/boards/msba2/Makefile.include
        /home/kijewski/RIOT/RIOT/boards/msba2-common/Makefile.include
        /home/kijewski/RIOT/RIOT/boards/msba2-common/Makefile.dep
        /home/kijewski/RIOT/RIOT/cpu/lpc2387/Makefile.include
        /home/kijewski/RIOT/RIOT/cpu/arm_common/Makefile.include
        /home/kijewski/RIOT/RIOT/cpu/lpc_common/Makefile.include
        /home/kijewski/RIOT/RIOT/Makefile.dep
        /home/kijewski/RIOT/RIOT/Makefile.cflags
        /home/kijewski/RIOT/RIOT/sys/Makefile.include
        /home/kijewski/RIOT/RIOT/drivers/Makefile.include
        /home/kijewski/RIOT/RIOT/Makefile.buildtests
```
core: imply current_prio in `sched_switch()`

There is no need to supply the current priority to `sched_switch()`,
when this function can easily tell the value of
`active_thread->priority` itself.
unittests: Force execution of $(UNITTEST_LIBS) build target
sys:transceiver: fix some doxygen comments
core:debug: documentation for `DEBUG_PRINT` was confusing and wrong
sys: add utility functions for `struct tm`
Add `struct tm` utility "test"
Merge pull request #1247 from thomaseichinger/transceiver_doc

sys:transceiver: fix some doxygen comments
Merge pull request #1146 from Kijewski/struct-tm-utils

sys: add utility functions for `struct tm`
Merge pull request #1209 from Kijewski/buildinfo

make: add comprehensive `buildinfo` list
tests: add missing license to test_struct_tm_utility
Merge pull request #1261 from Kijewski/test_struct_tm_utility-license

tests: add missing license to test_struct_tm_utility
pnet: accept should return a new generated file descriptor

From man page:
On success, these system calls return a nonnegative integer that is a
descriptor for the accepted socket. On error, -1 is returned, and errno
is set appropriately.
Merge pull request #1262 from cgundogan/fix_posix_accept

pnet: accept should return a new generated file descriptor
Merge pull request #1057 from Kijewski/sched_switch-current_prio

core: imply current_prio in `sched_switch()`
native: fix coding style
native: set optional path with unix socket option

fixes #1045
Merge pull request #1214 from LudwigOrtmann/issue-1045

native: unix socket path enhancement
Merge pull request #1238 from authmillenon/makefile-unittests

unittests: Force execution of $(UNITTEST_LIBS) build target
x86: fix download script for OSX

Mac OSX does not have `wget`, but `curl`.
It does not understand `tar xJ`, but `tar xj`.