Update test case for lifted GADT type rendering

The parsing of these seems to have been fixed by GHC folk and it now
renders differently. IMHO it now renders in a better way so I'm updating
the test to reflect this.
Don't shadow ‘strip’.

-Wall complains
Make ImplicitParams render correctly (#260)

This introduces a new precedence level for single contexts (because
implicit param contexts always need parens around them, but other types
of contexts don't necessarily, even when alone)
Lower precedence of equality constraints

This drops them to the new precedence pREC_CTX, which makes single
eqaulity constraints show up as (a ~ b) => ty, in line with GHC's
rendering. Additional tests added to make sure other type operators
render as intended. Current behavior matches GHC