Split RPL into core and mode related functions.
drivers - gpio: expanded gpio driver interface

- added functions for en|disabling a pins interrupt
driver - gpio: small adjustments
Merge pull request #1167 from fabianbrandt/rpl_base_split

Split RPL into core and mode related functions.
Merge pull request #1368 from haukepetersen/fix_gpio_disableinterrupt

drivers - gpio: expanded gpio driver interface
make: allow chosing ld-like over gcc-like options

make automatically adds '-Wl,' to linker-options. Supply `LINKFLAGPREFIX :=` to avoid that.
Merge pull request #1359 from backenklee/ldovergcclink2

make: allow chosing ld-like over gcc-like options
native: easify NATIVEINCLUDES usage
make: introduce source file blacklisting

Right now RIOT compiles in every source file it finds in the module
directory, unless the files were specified in `SRC` / `SRCXX`.

This PR adds the variables `SRC_BLACKLIST` and `SRC_WHITELIST`, which
might come in handy if your have conditional or mutual exclusive source
files as in #1350.