native/make/osx: circumvent unavailable gobjcopy

It's not used anyways, so just create an empty hex file if gobjcopy is
not found.
Merge pull request #2114 from LudwigOrtmann/native-osx-gobjcopy

native/make/osx: circumvent unavailable gobjcopy
travis: check PRs if they need squashing or depend on other PRs
Merge pull request #2090 from authmillenon/travis-squash-check

travis: squash check
drivers - netdev: extend netdev_state_t enum
drivers - cc110x: Initial import of new cc110x driver
boards - msbiot: prepare msbiot for new cc110x driver
Merge pull request #1772 from fnack/cc1101_if

drivers - cc110x: Propose new CC110x driver implementation
RIOT/Makefile.include: added variable `EXPECT_CONFLICT` to be used for indicating possibe conflicting features.
- For instance using `SPI0` and `DAC0` on the `stm32f4discovery` at the same time

The variable should be set in the board `Makefile.features`
[SQUASH ME or REMOVE ME] added small test
[SQUASH ME] added "groups" of conflicting features separated with ':',
            and made the conflict message optional
[SQUASH ME] added an initial readme
[SQUASH ME] added target/whitelist stm32f4discovery (only board with known conflicting features to me)