consistently use iSolveTC to solve typeclass goals
This avoids the proofmode to be irritated by unrelated goals with a typeclass type.
LambdaRust timings (on my laptop, and I've been browsing the web but hopefully Firefox didn't use too much CPU...): Before
real 13m17,543s
user 50m32,616s
sys 0m33,451s
After
real 13m3,314s
user 49m7,732s
sys 0m33,080s
So, if anything, this seems to help with performance.