Initial Support for new stdlib shift operator
Bugfix for non-const shift amt and unit tests.
Redesign after being hit with the KISS bat.
Add docs/generic impls
Tweak generic target.
Add shift support for generic-16 target.
Add shift support for knc targets.  This is not optimized.
Minor tweak for interface.
Make the new optimization play nicely with the other.s
Merge branch 'stdlibshift' of https://github.com/jbrodman/ispc into stdlibshift
remove condition.  Don't use gcc 4.7 for tests.
Source cleanup.
Add Performance Warning
Remove zero initialization for __vec4_i32
Merge pull request #641 from jbrodman/stdlibshift

Add a "shift" operator to the stdlib.