cex: display all the S/R conflicts, not just one per (state, rule)

Before this commit, on

    %%
    exp
    : "if" exp "then" exp
    | "if" exp "then" exp "else" exp
    | exp "+" exp
    | "num"

we used to not display the third counterexample below:

    Shift/reduce conflict on token "+":
      Example              exp "+" exp . "+" exp
      First derivation     exp ::=[ exp ::=[ exp "+" exp . ] "+" exp ]
      Second derivation    exp ::=[ exp "+" exp ::=[ exp . "+" exp ] ]

    Shift/reduce conflict on token "else":
      Example              "if" exp "then" "if" exp "then" exp . "else" exp
      First derivation     exp ::=[ "if" exp "then" exp ::=[ "if" exp "then" exp . ] "else" exp ]
      Second derivation    exp ::=[ "if" exp "then" exp ::=[ "if" exp "then" exp . "else" exp ] ]

    Shift/reduce conflict on token "+":
      Example              "if" exp "then" exp . "+" exp
      First derivation     exp ::=[ exp ::=[ "if" exp "then" exp . ] "+" exp ]
      Second derivation    exp ::=[ "if" exp "then" exp ::=[ exp . "+" exp ] ]

    Shift/reduce conflict on token "+":
      Example              "if" exp "then" exp "else" exp . "+" exp
      First derivation     exp ::=[ exp ::=[ "if" exp "then" exp "else" exp . ] "+" exp ]
      Second derivation    exp ::=[ "if" exp "then" exp "else" exp ::=[ exp . "+" exp ] ]

* src/counterexample.c (counterexample_report_state): Don't stop of
the first conflicts.
* tests/conflicts.at, tests/counterexample.at, tests/diagnostics.at,
* tests/report.at: Adjust.

tests/report.at

@@ -1190,6 +1190,16 @@ Shift/reduce conflict on token "⊕":
   First derivation     exp ::=[ exp ::=[ exp "⊕" exp • ] "⊕" exp ]
   Second derivation    exp ::=[ exp "⊕" exp ::=[ exp • "⊕" exp ] ]
 
+Shift/reduce conflict on token "+":
+  Example              exp "⊕" exp • "+" exp
+  First derivation     exp ::=[ exp ::=[ exp "⊕" exp • ] "+" exp ]
+  Second derivation    exp ::=[ exp "⊕" exp ::=[ exp • "+" exp ] ]
+
+Shift/reduce conflict on token "+":
+  Example              exp "⊕" exp • "+" exp
+  First derivation     exp ::=[ exp ::=[ exp "⊕" exp • ] "+" exp ]
+  Second derivation    exp ::=[ exp "⊕" exp ::=[ exp • "+" exp ] ]
+
 input.y:6.3-13: warning: rule useless in parser due to conflicts [-Wother]
 ]])
 
@@ -1377,6 +1387,20 @@ State 8
       First derivation         exp ::=[ exp ::=[ exp "⊕" exp • ] "⊕" exp ]
       Second derivation        exp ::=[ exp "⊕" exp ::=[ exp • "⊕" exp ] ]
 
+    Shift/reduce conflict on token "+":
+        1 exp: exp "⊕" exp •
+        2 exp: exp • "+" exp
+      Example                  exp "⊕" exp • "+" exp
+      First derivation         exp ::=[ exp ::=[ exp "⊕" exp • ] "+" exp ]
+      Second derivation        exp ::=[ exp "⊕" exp ::=[ exp • "+" exp ] ]
+
+    Shift/reduce conflict on token "+":
+        1 exp: exp "⊕" exp •
+        3 exp: exp • "+" exp
+      Example                  exp "⊕" exp • "+" exp
+      First derivation         exp ::=[ exp ::=[ exp "⊕" exp • ] "+" exp ]
+      Second derivation        exp ::=[ exp "⊕" exp ::=[ exp • "+" exp ] ]
+
 ]])