rearrange how we handle "constraint"
Copy parent's type coercions over if coercion is requested

Child types do not inherit constraints from their parent, for reasons we need
not go into here.  However, often the option 'constraint' is used to make a
minor tweak to an existing constraint where we do want the parent coercions to
still work.  (e.g. isa => File, constraint => sub { $_->stat }, coerce => 1)

For this, if simple coercion is requested (that is, the coerce option is true
and eq "1") and the parent type has coercions, we copy the coercions.  Any
errors (e.g. someone request coercions but the parent "isa" type has none) we
leave to Moose proper to blow up over.
a couple additional "did it actually die?" tests for inline subtyping
test coercion retention

On creating an anonymous subtype via "constraint", keep our coercions from the
parent type.
better document the constraint option

Show it requiring an isa be specified, and also how it will interact if
coercion is requested.  This can be a tricky area if you think about it too
much, so don't do that.
doc spelling corrections...

...and move the =for Pod::Coverage up to right below __END__ to be consistent.
v0.018

	* ~~ TRIAL ~~
	* If a constraint coderef is given and coercion is requested, we now copy
	  the parent type's coercions to the anonymous child type.
	* Better document the constraint option and how it interacts with simple
	  coercion.