Remove wc_insol from WantedConstraints

This patch is a pure refactoring, which I've wanted to do for
some time.  The main payload is

* Remove the wc_insol field from WantedConstraints;
  instead put all the insolubles in wc_simple

* Remove inert_insols from InertCans
  Instead put all the insolubles in inert_irreds

* Add a cc_insol flag to CIrredCan, to record that
  the constraint is definitely insoluble

Reasons

* Quite a bit of code gets slightly simpler
* Fewer concepts to keep separate
* Insolubles don't happen at all in production code that is
  just being recompiled, so previously there was a lot of
  moving-about of empty sets

A couple of error messages acutally improved.

1 files changed, 2 insertions, 2 deletions

diff --git a/testsuite/tests/warnings/should_fail/CaretDiagnostics1.stderr b/testsuite/tests/warnings/should_fail/CaretDiagnostics1.stderr
index 15dedf0516..532ca18ffc 100644
--- a/testsuite/tests/warnings/should_fail/CaretDiagnostics1.stderr
+++ b/testsuite/tests/warnings/should_fail/CaretDiagnostics1.stderr
@@ -1,6 +1,6 @@
 
 CaretDiagnostics1.hs:(5,3)-(7,16): error:
-    • Couldn't match expected type ‘IO a1’ with actual type ‘Int’
+    • Couldn't match expected type ‘IO a0’ with actual type ‘Int’
     • In a stmt of a 'do' block:
         10000000000000000000000000000000000000 + 2 + (3 :: Int)
       In the expression:
@@ -45,7 +45,7 @@ CaretDiagnostics1.hs:8:31-44: error:
   |                               ^^^^^^^^^^^^^^
 
 CaretDiagnostics1.hs:13:7-11: error:
-    • Couldn't match expected type ‘a0 -> a0’ with actual type ‘[Char]’
+    • Couldn't match expected type ‘a1 -> a1’ with actual type ‘[Char]’
     • In the pattern: "γηξ"
       In a case alternative: "γηξ" -> () '0'
       In the expression: case id of { "γηξ" -> () '0' }