Add bit-widths to pnacl targets in apps.
Add some export qualifiers for tests that use lowering and IR visitors.
Remove enforced c++98 from nightly tests.
Force C++11 for LLVM3.6
Turn on CXX11 for the nightly builds
Fix pnacl HL_TARGET strings for real this time
LLVM3.6's ObjectFile API changed yet again.
Changes to the makefile to get the nightly tests to pass

1) Add -lcuda and similar for the gpu tests

2) Don't build the generators with build_tests. build_tests
doesn't currently run any Halide code. I.e. it's supposed to
build the generators, but not run them yet. With this change
it does neither, which isn't ideal.
Generator::target defaults to get_host_target
Merge pull request #537 from halide/target=host

Generator::target defaults to get_host_target
halide_type_enum_map -> get_halide_type_enum_map()

I don’t think there are any current usages that could trigger the
static initialization order fiasco, but this change should forestall
future ones
Fixed an issue in the normalization of if and select nodes, where let's were not being correctly reapplied after visiting.
Merge branch 'master' into specialize_branched_loops
Fixed an issue in specialize branched loops, where chekcing for an equivalent branch point failed too early when a pervious branch point couldn't be comapred against.
Fixed a bug in specialize_branched_loops where I was using the wrong index to reference an element of an array. Also removed some changes that I had not meant to leave in permanently in my last commit.