Messed with the schedule for interpolate some more
Bounds inference more aggressive

Previously it was giving up on const expressions, instead of
just returning them
Found several bugs in clamped load detection. Disabled for now.
Don't lift out calls to current_time

Need a better solution for side-effecting calls in the future.
Added a vector test case to IRMatch
Track alignment info more reliably during simplification
Tweaks to tutorial lesson 2
Added a test case for reduction with dynamic bounds
CheckVars was traversing lets incorrectly
Fixed and reenabled clamped vector load
Merge branch 'master' into clamped-vector-load