With this, we're now using initializer requirements rather than
"convertFromXXX" requirements everywhere, addressing the rest of
rdar://problem/18154091. r22176 eliminated the performance penalty
that prevented this change from sticking earlier.
Swift SVN r22177
The initializer requirement is causing too much exponential behavior
in the constraint solver. We'll have to address that
first. Re-instating this change is tracked by rdar://problem/18381811.
Swift SVN r22080
With this, we're now using initializer requirements rather than
"convertFromXXX" requirements everywhere, addressing the rest of
rdar://problem/18154091.
Swift SVN r22078
