uhd: unexposed usrp_sink::get_device() and usrp_source::get_device() from SWIG

* multi_usrp class is not exposed to SWIG, so function returned a SwigPyObject and caused a memory leak when Python exits
* It is not practical to expose multi_usrp to SWIG, so simply tell SWIG to ignore it
volk: cmake: Rename GrBoost to VolkBoost to differentiate it from GR's GrBoost. Although they set the same BOOST variables internally, this change make it clear which cmake file to include.
cmake: Include GrBoost at the top level such that the correct default BOOST variables are set throughout the build. Because of the way CMake handles non-cached variables, each GR component (e.g., Volk) can change the BOOST variables for its particular needs without overriding these default values for other components.
digital: expose set_constellation message port in GRC for constellation_receiver.

Also cleans up white spaces.
blocks: adding a message port to the copy block to enable/disable copy.
digital: adding a rotate_phase message for the constellation_receiver to adjust the phase of the constellation.

Addresses Issue #599.
blocks.head: added callback to GRC definition
qtgui: Mostly adds sunset and cool color schemes for waterfall/raster plots.
qtgui: adds an alternative qss file.
qtgui: minor mods, including putting min/max lines in FFT sink behind all other lines.
qtgui: allows toggling rf frequencies on/off in GRC options box.

Addresses Issue #673.
qtgui: for sink_x, waterfall_sink_x, and freq_sink_x, when the display is double-clicked, the center frequency is adjusted to the clicked frequency and a message is posted containing the new center frequency.

Should be able to connect this to a radio message port input that will adjust the frequency of the device itself.
qtgui: freq, waterfall, and sink blocks produce a frequency message when double-clicked. Also can take in a frequency message to adjust the x-axis.
filter: adds a message input port to frequency xlating FIR filter to update the frequency.

The FFT version does not have this message port since it's a hierarchical block and there isn't an easy way to manage this.
docs: adding docs for blocks::copy and digital::constellation_receiver to describe their message ports.
qtgui: dynamically adjust min/max amplitude for qtgui freq and waterfall plots.

This is best achieved by using QTGUI Range variables to provide sliders for the upper and lower bounds.
add attributes for clang compiler
cmake: runtime: On Darwin, malloc is always aligned to a 16 byte boundary, to work with Altivec and SSE (etc) SIMD; so, set ALIGNED_MALLOC to 16 for those Darwin systems that do not have posix_memalign.
runtime: fix comment in posix_memalign.
tag_checker.h: fix unitialized d_has_next_tag; coverity 1128348

keeping style-compatible with the original file, just to keep the commit small