Bug #55582 mtr root detection (and if-expression execution) broken

if() treated any non-numeric string as false
Fixed to treat those as true instead
Added some test cases
Fixed missing $ in variable name in include/mix2.inc

mysql-test/include/mix2.inc

@@ -1910,7 +1910,7 @@ select hex(s1) from t4;
 drop table t1,t2,t3,t4;
 }
 
-if (test_foreign_keys)
+if ($test_foreign_keys)
 {
 eval create table t1 (a int primary key,s1 varbinary(3) not null unique) engine=$engine_type;
 eval create table t2 (s1 binary(2) not null, constraint c foreign key(s1) references t1(s1) on update cascade) engine=$engine_type;
@@ -2405,7 +2405,7 @@ drop table t1, t2, t3, t5, t6, t8, t9;
 }
 # End transactional tests
 
-if (test_foreign_keys)
+if ($test_foreign_keys)
 {
 # bug 18934, "InnoDB crashes when table uses column names like DB_ROW_ID"
 --error 1005

mysql-test/r/mysqltest.result

@@ -393,6 +393,8 @@ true-inner again
 true-outer
 Counter is greater than 0, (counter=10)
 Counter is not 0, (counter=0)
+Counter is true, (counter=alpha)
+Beta is true
 1
 Testing while with not
 mysqltest: In included file "MYSQLTEST_VARDIR/tmp/mysqltest_while.inc": At line 64: Nesting too deeply

mysql-test/t/mysqltest.test

@@ -1105,6 +1105,25 @@ if (!$counter)
   echo Counter is not 0, (counter=0);
 }
 
+# ----------------------------------------------------------------------------
+# Test if with some non-numerics
+# ----------------------------------------------------------------------------
+
+let $counter=alpha;
+if ($counter)
+{
+  echo Counter is true, (counter=alpha);
+}
+let $counter=   ;
+if ($counter)
+{
+  echo oops, space is true;
+}
+if (beta)
+{
+  echo Beta is true;
+}
+
 # ----------------------------------------------------------------------------
 # Test while, { and }
 # ----------------------------------------------------------------------------