Integrated changes from mmp/and-fold-opt:

Add peephole optimization to eliminate some mask AND operations.

On KNC, the various vector comparison instructions can optionally
be masked; if a mask is provided, the result is effectively that
the value returned is the AND of the mask with the result of the
comparison.

This change adds an optimization pass to the C++ backend that looks
for vector ANDs where one operand is a comparison and rewrites
them--e.g. "and(equalfloat(a, b), c)" is changed to
"_equal_float_and_mask(a, b, c)", saving an instruction in the end.

Issue #319.

Merge commit '8ef6bc16364d4c08aa5972141748110160613087'

Conflicts:
	examples/intrinsics/knc.h
	examples/intrinsics/sse4.h

examples/intrinsics/generic-32.h

@@ -265,6 +265,15 @@ static FORCEINLINE __vec32_i1 NAME##_##SUFFIX(TYPE a, TYPE b) {     \
    for (int i = 0; i < 32; ++i)                                     \
        ret.v |= ((CAST)(a.v[i]) OP (CAST)(b.v[i])) << i;            \
    return ret;                                                      \
+}                                                                   \
+static FORCEINLINE __vec32_i1 NAME##_##SUFFIX##_and_mask(TYPE a, TYPE b,       \
+                                              __vec32_i1 mask) {    \
+   __vec32_i1 ret;                                                  \
+   ret.v = 0;                                                       \
+   for (int i = 0; i < 32; ++i)                                     \
+       ret.v |= ((CAST)(a.v[i]) OP (CAST)(b.v[i])) << i;            \
+   ret.v &= mask.v;                                                 \
+   return ret;                                                      \
 }
 
 #define INSERT_EXTRACT(VTYPE, STYPE)                                  \