Merge pull request #369 from jduprat/master

Task system updates
Fix crash when using launch with non-task-qualified function
Implement the KNC prefetch API so that ISPC prefetch_*() stdlib functions may be used.
Minor fixes needed for building on windows.
Switch to LLVM 3.1 for default for MSVC builds.  Also fixes issue #374
Issue error if a vector-typed parameter is used in an exported function.

Issue #363.
Updated user's guide to comply with Intel® Xeon Phi™ brand usage guidelines
Updated usage of Initial Many Core Instructions (Intel® IMCI) instructions.
Merge branch 'master' of https://github.com/ispc/ispc
Fix crasher with malformed programs
Improve naming of temporary variable in IR
Fix bugs with handling of 'continue' statements in foreach_* loops.
Use LLVM_VERSION env variable to get LLVM version with MSVC build.

Previously, it was set directly in the ispc.vcxproj file.

Issue #371.
Add files inadvertently missed in c58d92d46bd6.

Truly fixes issue #363.
two changes:
- exported structs now get protected with #ifdef/#define blocks (allows including multiple ispc-generated header fiels into the same c source
- when creating offload stubs, encountering a 'export' function for which we cannot produce a stub will only trigger a warning, not an error.
Added the following mask tests: __any(), __all(), __none() for all supported targets.
This allows for more efficient code generation of KNC.
Don't force loads/stores from varying types to be unaligned.

These should always actually be aligned in memory.
Mark __any(), __all(), and __none() as internal after they're linked in.

This fixes multiple symbol definition errors when compiling a single binary
for multiple ISA targets.
Add --opt=force-aligned-memory option.

This forces all vector loads/stores to be done assuming that the given
pointer is aligned to the vector size, thus allowing the use of sometimes
more-efficient instructions.  (If it isn't the case that the memory is
aligned, the program will fail!).
#define ISPC_FORCE_ALIGNED_MEMORY, if appropriate, in C++ output.