Replace global-scope helpers finToNat and finToInteger with functions whose type signatures match the names.
Add FinZAbsurd and FinZElim.
Replace Prelude.Vect.take and Prelude.Vect.drop with versions of a saner type signature.
Replace Prelude.Vect.intersperse with a saner-typed version. Make intersperse' a proper helper function (non-exported).
Check data declarations for redefinition

It's okay if the previous definition is a type declaration and the
type is unchanged. Otherwise, it's an attempt at redefinition and
is now reported as an error.

Fixes #693
Give names for clauses generated with :addmissing

Names generated using the same machinery/heuristics as ordinary
case split generation.
Merge branch 'prelude_cleanup' of https://github.com/sjdrodge/Idris-dev into sjdrodge-prelude_cleanup
Bracket output of \o if necessary
Minor fix for variable update in case split
Set version to 0.9.10.1
Remove tutorial from idris.cabal