Add tests for E-needstest issues
Propagate coercions through match expressions.
auto merge of #19769 : nick29581/rust/coerce-if, r=nikomatsakis

r? @nikomatsakis 

We discussed coercions for `if` and `match` expressions. `if` seems to work already, was there some specific behaviour which wasn't working?
auto merge of #19780 : jakub-/rust/e-needstest, r=alexcrichton

Closes #5988.
Closes #10176.
Closes #10456.
Closes #12744.
Closes #13264.
Closes #13324.
Closes #14182.
Closes #15381.
Closes #15444.
Closes #15480.
Closes #15756.
Closes #16822.
Closes #16966.
Closes #17351.
Closes #17503.
Closes #17545.
Closes #17771.
Closes #17816.
Closes #17897.
Closes #17905.
Closes #18188.
Closes #18232.
Closes #18345.
Closes #18389.
Closes #18400.
Closes #18502.
Closes #18611.
Closes #18783.
Closes #19009.
Closes #19081.
Closes #19098.
Closes #19127.
Closes #19135.
Merge remote-tracking branch 'upstream/master'